Sprinkle chicken with half of the chili powder and salt. Grill chicken with 1 tsp oil until golden-brown and juices run clear when chicken is pierced, about 15 minutes. Let chicken cool and cut into strips or cubes.
Meanwhile cook red and green peppers, onion and garlic with 1 tsp of oil in a skillet on medium heat adding remaining chili powder and salt. Stir occasionally and cook until tender, about 4 minutes. Stir in salsa and lime juice.
Mound vegetable mixture, chicken, avocado slices and lettuce on tortillas, roll up and serve.