In a bowl, combine olive oil, chili powder, cumin, garlic powder, salt, and pepper.
Add the sliced chicken to the marinade and let it sit for 10 minutes.
Heat a grill or skillet over medium-high heat.
Add the marinated chicken to the skillet and cook for 5-7 minutes until browned and cooked through.
Remove the chicken and set aside.
In the same skillet, add the sliced onions and bell peppers.
Sauté for 5-7 minutes until the vegetables are tender and slightly charred.
Slice the cooked chicken into strips and return it to the skillet.
Toss everything together and cook for an additional 2-3 minutes.
Serve hot with warm tortillas.