In a bowl, mix olive oil and fajita seasoning.
Add sliced chicken to the bowl and coat evenly.
Heat a large skillet over medium-high heat.
Add the seasoned chicken to the skillet and cook for 5-7 minutes until browned.
Remove chicken from the skillet and set aside.
In the same skillet, add sliced onions and bell peppers.
Sauté for 4-5 minutes until vegetables are tender.
Return the chicken to the skillet and mix with vegetables.
Cook for an additional 2-3 minutes to heat through.
Serve immediately with warm tortillas and toppings.