1. Rinse chicken, pat dry, and cut into 1/2-inch pieces.
2. In a 10- to 12-inch nonstick frying pan over high heat, combine oil, onion, carrots, garlic, and cumin; stir often until onion is lightly browned, about 5 minutes. Pour into a bowl.
3. Add chicken to pan and stir often until no longer pink in center of thickest part (cut to test), about 5 minutes. Pour onion-carrot mixture back into pan and stir until hot, 1 to 2 minutes.
4. Spoon chicken mixture onto tortillas. Add sour cream, cheese, salsa, and salt and pepper to taste. Fold tortillas around filling to eat.