If you’ve never swapped burger buns for portobello mushrooms before, get ready to fall a little bit in love. These Portobello Mushroom Bun Burgers are juicy, messy in the best way, and loaded with creamy homemade guacamole that ties everything together. The mushrooms get tender and savory as they cook, giving you all the satisfaction of a classic burger but with a fun, veggie-forward twist.
Olivia’s Personal Note
We love a classic burger with buns, like my turkey burgers or my go-to hamburger recipe.
But I’m also a huge fan of bunless burgers! If you’ve tried my Spinach Sauce Bunless Burger (made with homemade mayo, spinach, and avocado… truly to die for!), or my Bunless Turkey Burger and Bunless Burgers Recipe, you already know how good they can be.
So today, I’m excited to share these Portobello Mushroom Bun Burgers with Guacamole. They’re bunless too, but the portobello “buns” work so well here. It’s such a fun idea, right? And the guacamole on top just takes everything to the next level. So much flavor in every bite.
These burgers are incredibly flavorful and pair perfectly with my Air Fryer Sweet Potato Fries. Total weeknight win!
Key Ingredients:
Portobello Mushroom Caps — I’ve tested these mushroom “buns” so many times, and they’re honestly such a fun twist. When you remove the gills and roast or grill them, they get tender, juicy, and hold the burger together surprisingly well. Every time I make this, people are shocked by how satisfying they are.
Ground Beef — I’ve tried this recipe with turkey and chicken too, but ground beef burgers always gives the juiciest, most flavorful patty. It balances so well with the mushrooms and guacamole. It’s that classic burger feel… just without the bread.
Avocado — I’ve made this homemade guacamole version over and over again, and a ripe avocado is truly the key. When it’s perfectly soft, it mashes into the creamiest topping and gives the whole burger that fresh, bright flavor.
Red Onion — I’ve added red onion to this recipe so many times because it adds that crunchy, sharp bite that balances all the rich, creamy flavors. Even a few thin slices make such a difference.
Olive Oil — I’ve used olive oil every time to coat the mushrooms and help them get that gorgeous golden edge. It keeps everything juicy and adds a subtle richness.
How to clean Portobello mushrooms:
This is something very simple to do, but a very important step to have a delicious mushroom bun since they tend to come a bit dirty from the stores. You are just going to do a quick cleaning.
- First, you’re going to gently twist off the stem of each mushroom. The stem is delicious too, so I recommend saving it to sauté and add in your omelette or frittata for example.
- Then, hold the mushroom cap in one hand and use a spoon to scrape out all the gills from the underside of the Portobello mushroom cap. The gills, in my opinion, are not great to eat, so you can discard them. Now, they are ready to grill. Simple and easy!
How to grill a Portobello mushroom:
Now that your mushrooms are clean and ready to cook you need to marinate them before you grill them. Doing this first will make the mushroom buns much more flavorful.
- First, you will place all the ingredients for the Portobello Mushroom Buns in a small bowl and mix everything well to combine.
- Then, you will add the cleaned mushroom caps in the bowl and coat them with the olive oil mixture and let stand for 1 hour.
- Now, oil the grill or grill pan and bring the heat to medium.
- Add the Portobello to the grill and cook for 4 minutes or so. Using tongs, carefully flip the mushroom to the other side and grill for more 4 minutes.
Olivia’s Recipe Tips
1. Chill the patties before cooking
This is optional but if you have time, pop your burgers in the fridge for 15 minutes. This keeps them firm and helps you get that gorgeous, golden crust.
2. Add a tiny splash of Worcestershire or tamari
Just a little boosts the “umami” and makes the burgers taste restaurant-level without extra work.
3. Don’t over-mix the meat
Think “gentle hands.” The more you squish the meat, the tougher the burger gets.
4. Make a small thumbprint in the center
This helps the burgers cook evenly and stay flat instead of puffing up in the middle.
Portobello Mushroom Bun Burgers
Ingredients
For the Guacamole
- 1 avocado
- 1/3 cup red bell pepper finely chopped
- 2 tablespoons diced tomatoes
- ½ red onions chopped
- 1 garlic clove minced
- 1 tablespoon lime juice
- Salt and black pepper
- 1 tablespoon fresh cilantro chopped
For the Burger
- 1 lb ground beef
- 1 egg
- ¾ cup white onions chopped
- Salt and black pepper to taste
- ¼ teaspoon Dijon mustard
- 1 teaspoon garlic powder
- 2 teaspoons extra virgin olive oil
For the Portobello Mushroom Buns
- 2 tablespoons olive oil
- Salt and black pepper
- 1 garlic clove minced
- 8-12 Portobello Mushroom stems and gills removed
For Serving
- Slices of red onions tomatoes, cooked bacon and microgreen leaves or any other green leaves you prefer to serve.
Instructions
- Make the spinach sauce: Add avocado in a bowl and mash it with a fork. Add all the ingredients and stir well. Set aside.
- Place all the ingredients for the mushroom buns in a bowl, except for the mushrooms. Mix well. Add the mushroom into the olive oil mixture bowl and coat them well. Set aside for about 1 hour. Place “buns” on grill and let them cook for 4 minutes.
- To make the burger, combine all ingredients, except the olive oil, in a large bowl. Mix everything well to combine and using your hands divide the mixture into 4-6 burgers.
- Heat the olive oil in a non-stick grill pan (or simply cook your burger in a BBQ) over a medium-high heat. Cook the burger for 3-5 minutes on each side, or until reach 145°F for medium-rare or 160°F for well-done. Set them aside.
- To build each burger, top one Portobello mushroom guacamole, patty burger, more guacamole, two slices of red onions, 2 slices of bacon, 2 slices of tomatoes and some microgreen or leaves. Top with second Portobello mushroom ban.
Notes
- Do not overmix the meat, as it’ll lead to a dense and tough patty.
- Avoid squeezing the patties together tightly as you don’t want the patties to be dense.
- Make sure you don’t rush the mushrooms as you want them to grill all the way through or the texture won’t be as good.
- To store: Keep leftover burger patties in the fridge in an airtight container for up to 5 days. Store the mushrooms in a separate container. The guacamole also needs to be stored separately. The guac may brown over time.
- To reheat: Reheat the beef burgers on the grill or in the microwave.
- To freeze: Flash freeze the raw patties before transferring them to a freezer-safe bag and freeze for up to 3 months.
Nutrition
Nutrition information is automatically calculated, so should only be used as an approximation.
Did You Make This?
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Que delícia
Tava mesmo. Eu e Pierre comemos uns dois cada hahahaha.
Typo noted. “For the spinach sauce…” I think you meant guacamole sauce!
You’re totally right. Thanks for pointing that out. I just fixed that.
what is the calorie count?
Just added it for you. Thanks for asking.
The recipe says to grill the mushrooms for 4-5 minutes but up above you say 4 per side. Can you clarify?
It’s 4 mins or so. It depends on how much cooked you prefer your mushroom to be.