Rinse the rice under cold water. In a medium saucepan, combine the rice and water or beef broth. Bring to a boil, then reduce heat to low, cover, and let simmer for about 15-20 minutes until the rice is cooked and the liquid is absorbed. Fluff with a fork and set aside.
In a large skillet over medium-high heat, add the ground beef. Cook, breaking it apart with a wooden spoon, until browned (about 5-7 minutes). Drain any excess fat.
Stir in the taco seasoning mix and add ¼ cup of water. Cook for another 5 minutes until the beef is well-coated with the seasoning and heated through. If needed, add salt and pepper to taste.
Add the black beans, corn, and diced tomatoes to the skillet with the seasoned beef. Stir well and cook for an additional 5 minutes until everything is heated through.
To assemble the Taco Rice Bowls, start by placing a portion of cooked rice at the bottom of each serving bowl. Top with the beef mixture, followed by shredded lettuce, cheese, sour cream, and diced avocado.
Drizzle with taco sauce or salsa if desired, serve immediately and enjoy your delicious Taco Rice Bowls!