Slice the chicken or steak into thin strips.
In a bowl, combine the meat with olive oil and fajita seasoning.
Heat a skillet over medium-high heat.
Add the seasoned meat to the skillet and cook until browned (about 5-7 minutes).
Remove the meat from the skillet and set aside.
In the same skillet, add sliced bell peppers and onion.
Sauté the vegetables until they are tender (about 5 minutes).
Return the cooked meat to the skillet and mix with the veggies.
Warm the tortillas in a separate pan or microwave.
Serve the meat and vegetable mixture on the tortillas, garnished with cilantro.