Preheat your grill or grill pan over medium-high heat. In a small bowl, mix together olive oil, chili powder, cumin, garlic powder, onion powder, salt, and black pepper. Rub this mixture all over the chicken breasts.
Grill the chicken for about 6-7 minutes per side, or until fully cooked and internal temperature reaches 165°F. Remove from the grill and let it rest for 5 minutes before slicing.
In a separate bowl, combine ranch dressing and chipotle sauce. Adjust the chipotle sauce to your desired spice level.
To assemble the burritos, lay a tortilla flat and add 1/2 cup of cooked rice in the center. Top with sliced grilled chicken, 1/4 cup black beans, 1/4 cup corn, diced tomatoes, a few slices of avocado, and a sprinkle of shredded cheese.
Drizzle about 2 tablespoons of the chipotle ranch sauce over the fillings. Fold in the sides of the tortilla and roll it up tightly from the bottom to the top. Repeat with remaining tortillas and fillings.
If desired, grill the assembled burritos for an additional 2-3 minutes on each side to crisp up the tortilla and melt the cheese inside.
Slice in half, garnish with fresh cilantro if using, and serve with extra chipotle ranch sauce on the side.