Cut chicken crosswise into 5 or 6 strips. Toss with half the oil; add lime juice, chili powder and cumin; set aside.

Combine onions and peppers in prepared roasting pan. Drizzle with remaining oil; sprinkle with salt and pepper. Add chicken mixture; stir to combine and spread out in the pan. Roast in preheated oven, stirring once or twice, for 20 to 25 minutes or until chicken is no longer pink inside and vegetables are tender.

Meanwhile, wrap tortillas tightly in foil and place in the oven for 10 minutes to heat.

Transfer chicken and vegetables to a heated platter and serve with tortillas, lettuce, avocados, salsa, and sour cream. Have each diner spoon some chicken mixture into a tortilla, top with lettuce, avocado, salsa, and sour cream to taste; roll up to eat.