Spinach, Mushroom and Cheese Quesadillas

Name: Spinach, Mushroom and Cheese Quesadillas
Cuisine: American, Mexican, Latin American
Ingredients: 6 tablespoons unsalted butter; 6 ounces mushrooms, thinly sliced (2 cups); Salt and freshly ground pepper; 1 large zucchini, coarsely chopped; One 10-ounce package frozen chopped spinach, thawed and squeezed dry; 1 tablespoon extra-virgin olive oil; 1 medium white onion, finely chopped; 1 garlic clove, minced; 2 medium jalapeños, seeded and finely chopped; 1 teaspoon dried oregano; 1/4 cup finely chopped black olives; 1/2 cup grated cotija cheese or crumbled feta; 3 ounces mozzarella cheese, shredded (3/4 cup); Eight 8-inch flour tortillas; Sour cream, for serving