Preheat your grill or stovetop grill pan over medium-high heat.

In a small bowl, mix together the olive oil, chili powder, cumin, garlic powder, onion powder, salt, and pepper. Rub the spice mixture all over the chicken breasts.

Grill the chicken for about 6-7 minutes on each side, or until the internal temperature reaches 165°F. Remove from the grill and let it rest for 5 minutes before slicing.

While the chicken is resting, prepare the bowls. In a large bowl, combine the cooked brown rice, black beans, corn, cherry tomatoes, and diced avocado.

Squeeze lime juice over the mixture and toss gently to combine.

Divide the rice and bean mixture into serving bowls. Top each bowl with sliced grilled chicken, shredded cheddar cheese, and chopped cilantro.

Serve with a dollop of sour cream or Greek yogurt, if desired.