In a bowl, combine olive oil, chili powder, garlic powder, cumin, salt, and pepper.
Add sliced chicken to the marinade, mixing well to coat.
Let the chicken marinate for at least 10 minutes.
Heat a skillet over medium-high heat.
Add the marinated chicken to the skillet and cook for about 5-7 minutes, until cooked through.
Remove the chicken and set aside.
In the same skillet, add sliced onions and bell peppers.
Cook for 5-7 minutes until they are tender.
Return the chicken to the skillet and mix with the vegetables.
Serve immediately with warm tortillas and toppings of your choice.