In a large skillet, heat the olive oil over medium heat. Add the diced onion and cook for about 3-4 minutes until softened. Add the minced garlic and cook for an additional minute until fragrant.
Add the ground beef or turkey to the skillet. Cook until browned, breaking it apart with a spatula, about 5-7 minutes. Drain any excess fat.
Stir in the taco seasoning, black beans, corn, and diced tomatoes. Cook for another 5 minutes, allowing the flavors to meld. Season with salt and pepper to taste.
To assemble the taco rice bowls, start with a base of cooked rice in each bowl. Top with the taco mixture, followed by shredded lettuce, cheddar cheese, sour cream, salsa, and avocado slices.
Serve immediately and enjoy your delicious taco rice bowls!