In a large bowl, combine the beef stew meat, green bell pepper, red bell pepper, yellow onion, diced tomatoes, beef broth, soy sauce, Worcestershire sauce, garlic powder, and black pepper.
Transfer the mixture to a slow cooker.
Cook on low for 8 hours or on high for 4 hours.
If desired, thicken the sauce by whisking together cornstarch and water in a small bowl. Stir into the slow cooker during the last 30 minutes of cooking.
Serve over rice or noodles.
Notes
For a spicier dish, add a pinch of red pepper flakes.