Preheat your grill or stovetop grill pan over medium-high heat. Season the chicken breasts with salt, pepper, and ranch seasoning mix.
Grill the chicken for about 6-7 minutes per side, or until fully cooked and internal temperature reaches 165°F. Remove from heat and let it rest for 5 minutes before slicing.
In a large bowl, combine the cooked brown rice, corn, black beans, and cherry tomatoes. Mix well and season with salt and pepper to taste.
To assemble the bowls, divide the rice mixture among four bowls. Top each with sliced grilled chicken, diced avocado, and shredded cheddar cheese.
Drizzle additional BBQ sauce over the top and sprinkle with chopped cilantro. Serve with lime wedges on the side.