Rice: In a saucepan over medium heat, add the chicken broth, water, olive oil, 1 tablespoon lime juice and rice. Bring the mixture to a rapid boil and then reduce heat to low. Cover the mixture and cook for about 20-25 minutes, or until rice is tender.
Remove from heat and stir in the cilantro, remaining lime juice, salt and pepper.
Evenly distribute the mixture into 4 bowls. Top with equal amounts of lettuce, diced tomatoes (about 1-1/2 tablespoons), black beans (2 tablespoon), corn (2 tablespoon) & Chicken. Top with cheddar cheese, fresh cilantro, 1 teaspoon of red onion to each.
Make the Avocado mixture by mashing the flesh of one medium, ripe avocado, garlic powder, salt and 1 teaspoon lime juice until creamy. Divide evenly on the top of each bowl. Add sour cream, if desired.
Sprinkle the bowl with lime juice, salt and pepper.