Heat a skillet over medium heat. Add the ground beef, diced onion, and minced garlic. Cook until the beef is browned and the onion is soft. Drain any excess fat and transfer the mixture to the slow cooker.
Add the diced red bell pepper, black beans, diced tomatoes with green chilies, beef broth, chili powder, cumin, salt, and black pepper to the slow cooker. Stir everything together until well combined.
Cover the slow cooker and cook on low for 6 to 8 hours or on high for 3 to 4 hours until the flavors have blended and the mixture is hot throughout.
Spoon the beef and bean mixture over cooked rice in individual bowls. Let everyone add their own cheese, avocado, sour cream, and cilantro before eating.