Preheat your grill or grill pan over medium-high heat. In a small bowl, mix together the chili powder, garlic powder, onion powder, cumin, salt, and black pepper. Rub this spice mixture onto the chicken breasts.
Drizzle olive oil over the chicken and place it on the grill. Cook for about 6-7 minutes per 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 burrito fillings. In a large bowl, combine the cooked rice, black beans, corn, and chipotle ranch dressing. Mix well.
To assemble the burritos, lay a tortilla flat on a clean surface. Place a portion of the rice mixture in the center, followed by sliced grilled chicken, shredded lettuce, diced tomato, and shredded cheese.
Fold in the sides of the tortilla and then roll it up from the bottom to the top, ensuring all fillings are tucked inside. Repeat with the remaining tortillas and fillings.
If desired, heat a skillet over medium heat and place the burritos seam-side down to toast for 2-3 minutes on each side, until golden brown and crispy.
Serve with sour cream and chopped cilantro, if desired.