Heat olive oil in a large skillet over medium-high heat. Add sliced bell pepper and onion, cooking for 3-4 minutes until slightly softened.
Stir in the rotisserie chicken. Sprinkle with Fajita seasoning and the amount of water indicated on the package. Cook for 3-4 minutes, stirring occasionally, until heated through.
Warm the tortillas in the microwave or on a dry skillet. Divide the fajita mixture between the tortillas.
Top with shredded cheese, salsa, Greek yogurt, or avocado slices as desired.