As nouns the difference between fajita and quesadilla

is that fajita is a Tex-Mex dish of strips of spicy marinated meat and/or vegetables in a soft flour tortilla, often served with salad or a savoury filling while quesadilla is a Mexican dish made by filling a tortilla (corn or flour) with cheese, folding in half and toasting until the cheese is melted. Additional ingredients, such as meats (chicken or beef, commonly), or vegetables can be added. Often served with salsa, guacamole and/or sour cream.