Cook the Beef: In a large skillet over medium heat, add the ground beef.
Cook until browned, breaking it apart with a spatula, about 5-7 minutes. Drain excess fat if necessary.
Season the Beef: Add chili powder, cumin, salt, and pepper to the beef.
Stir well to combine and cook for another 2-3 minutes until the spices are fragrant.
Prepare the Base: While the beef is cooking, prepare the rice or quinoa according to package instructions.
Assemble the Bowl: In serving bowls, layer the cooked rice or quinoa, followed by the seasoned ground beef, black beans, corn, diced tomatoes, and avocado.
Garnish and Serve: Top with chopped cilantro, sour cream, and shredded cheese if desired. Serve immediately.