Heat half of the oil in a skillet or non-stick pan over medium heat. Add the onions and peppers, and season with salt and pepper. Sauté until onions are translucent and peppers are tender.
Add in the chicken, chili powder, cumin, lime juice, and season with salt and pepper. Saute until the chicken is nicely browned and fully cooked to an internal temperature of 160 degrees using a thermometer.
Heat the tortilla shells on both sides in a nonstick pan on medium heat to warm them up.
Portion the chicken, onions, and peppers, on the warmed tortilla. Roll up and garnish with cilantro. Serve with sour cream.