In a large skillet over medium heat, heat 1 tbsp. oil. Add the onions and peppers, and season with salt and pepper to taste. Cook until onions and peppers are tender, about 6 minutes. Add in the chicken, lime juice, chili powder, and cumin; sauté until the chicken is cooked through and no longer pink.
Add the corn and cook for 1 to 2 minutes.
Warm the taco shells on both sides in a nonstick pan on medium heat.
Garnish with cilantro, serve with sliced avocado and sour cream on the side.