Preheat oven to 400°F. Set aside a large baking sheet.
Place the onions and bell peppers on a work surface and slice into 1/2-inch wide pieces. Next, cut the chicken into 1/2-inch wide strips. Note: You may find it helpful to freeze the chicken for 30 minutes to firm the meat up for easier slicing.
Scatter the chicken, peppers, onions and peppers evenly across the baking sheet. Sprinkle cumin, chili powder, garlic, paprika, salt and pepper on top and drizzle with oil.
Using tongs or two spoons, toss all ingredients on the pan to coat evenly.
Bake for 15 minutes.
Remove from oven, and use tongs stir chicken and vegetables. Then slide them one-quarter of the way over, to make space for tortillas.
Mop up excess juices with a paper towel, and then add the tortillas to the pan. Return to the oven and bake for 5 more minutes.
Remove from oven and squeeze optional fresh lime on top. Serve in tortillas with optional cilantro, sour cream and avocado.