Preheat your grill or skillet over medium-high heat.
In a bowl, combine chicken, olive oil, chili powder, cumin, garlic powder, salt, and pepper.
Mix until chicken is evenly coated with spices.
Add sliced bell peppers and onions to the bowl, mixing them with the chicken.
Place the chicken and vegetables onto the grill or skillet.
Cook for about 5-7 minutes, stirring occasionally, until the chicken is cooked through.
Remove from heat and let it rest for a few minutes.
Warm the tortillas on the grill or in a separate skillet.
Spoon the chicken and vegetable mixture onto the tortillas.
Serve immediately with your choice of toppings.