In a bowl, combine the diced chicken breast with olive oil, lime juice, cumin, chili powder, salt, and pepper. Mix well and let it marinate for at least 30 minutes for enhanced flavor.
Grill the marinated chicken on medium-high heat until fully cooked, about 7-9 minutes. Remove from heat, let it rest for a few minutes, and then dice into bite-sized pieces.
If not already cooked, prepare brown rice according to package instructions. Fluff with a fork and set aside.
In a large serving bowl or individual bowls, layer the cooked rice as the base.
On top of the rice, add the grilled chicken, black beans, corn, diced red bell pepper, diced avocado, cherry tomatoes, and shredded lettuce.
Sprinkle shredded cheddar cheese and chopped cilantro on top for extra flavor.
Add a wedge of lime on the side for added zest and serve immediately while everything is fresh and vibrant.