Season the beef sirloin strips with salt and black pepper.
Add the sliced bell peppers, onions, garlic, and seasoned beef to the slow cooker. However, if you prefer your vegetables more crisp, add them during the last hour of cooking.
In a small bowl, mix the beef broth, soy sauce, Worcestershire sauce, honey, ground ginger, cornstarch and crumble in the beef bouillon cubes. Stir until the bouillon is dissolved.
Pour the sauce mixture over the beef and vegetables in the slow cooker. Stir to combine everything.
Cover and cook on low for 6-7 hours or on high for 3-4 hours, until the beef is tender and the vegetables are soft.
Once it’s cooked, taste and adjust seasoning if needed. Serve hot with rice, noodles, steamed broccoli or your favorite side.