Marinate the chicken breasts in olive oil, chili powder, cumin, salt, and pepper for at least 30 minutes.
Preheat your grill to medium-high heat.
Grill the marinated chicken for about 6-7 minutes per side, or until fully cooked.
Remove the chicken from the grill and let it rest for 5-10 minutes before slicing.
Slice the grilled chicken into strips.
Warm the tortillas on the grill or in a skillet until soft and pliable.
Assemble the burritos by layering sliced chicken, lettuce, tomato, avocado, and chipotle ranch dressing on each tortilla.
Fold in the ends of the tortilla and roll it tightly from one side to the other.
Serve the burritos immediately, with extra dressing on the side if desired.