Coat a nonstick frying pan with butter-flavored cooking spray.
Over medium heat, add shrimp and pan fry for 1 minute. Turn the shrimp, spraying the pan again if necessary, and cook until cooked through for 2 minutes. Drizzle shrimp with fajita spice (add more to taste, if desired).
Arrange a lettuce leaf, 2 tomato slices, and 3 shrimp on half of each tortilla. Fold the other half over the filling, pressing the tortilla edges together.
Coat a nonstick frying pan with butter-flavored cooking spray. In medium heat, add the quesadillas and fry 1 to 2 minutes or until lightly toasted on the bottom; then turn and fry the other side for 1 to 2 minutes or until golden.