Heat oil in a pan over medium heat. Add sliced bell peppers and onions to the pan.
Sprinkle taco seasoning, salt, and black pepper powder over the vegetables.
Saute the vegetables until they are tender yet still have a bit of crunch. This usually takes about 5-7 minutes.
Place a chapati or tortilla on a flat surface. Spoon a portion of the fajita filling onto one half of the chapati or tortilla.
Sprinkle a generous amount of shredded cheese over the filling. Fold the other half of the chapati or tortilla over the filling, creating a half-moon shape.
Heat a pan or griddle over medium heat. Place the assembled quesadilla on the hot surface.
Cook for 2-3 minutes on each side or until the tortilla is golden brown, and the cheese is melted. Remove the quesadilla from the pan and let it cool for a minute.
Slice it into wedges and serve with your favorite toppings, such as salsa, guacamole, or sour cream.