heat oil in a 10 to 12 inch nonstick skillet over medium-high heat. Add mushrooms and garlic. Cook until mushrooms release the liquid, 3 to 4 minutes. Stir in tomatoes, cook two more minutes. Season mushroom mixture with salt and pepper then transfer to a bowl. Wipe out skillet.
Assemble each tortilla with 1/2 cup cheese, 1/2 cup mushroom mixture, and 1 tablespoon shallots. Fold tortillas in half to cover filling. Spray skillet with nonstick spray.
Arrange two quesadillas in skillet. Cook over medium-high heat until cheese melts and tortillas Brown. Flip and cook other side. Remove quesadilla to a cutting board and cut into fourths. Repeat with remaining quesadillas.