In a large skillet, heat the olive oil over medium heat. Add the ground beef or turkey, breaking it apart with a spatula. Cook until browned, about 5-7 minutes. Drain excess fat if necessary.
Stir in the taco seasoning mix and follow the package instructions, usually adding a bit of water. Let it simmer for about 5 minutes until thickened.
In a large bowl, combine the cooked rice, black beans, corn, and diced tomatoes. Mix well and season with salt and pepper to taste.
To assemble the bowls, start with a base of the rice mixture. Top with the seasoned meat, shredded lettuce, cheddar cheese, sour cream, and diced avocado if using.
Finish by sprinkling crushed Doritos on top for added crunch. Serve immediately.