Heat oven to 400. In a large skillet heat about 3 tablespoons of olive oil over medium heat. Add onion, and a pinch of salt. Stir and cook until onions are soft then add garlic and cook for about 1 minute.
Add zucchini and corn. Stir and cook for about 6 mintues or until soft and tender. Remove from heat. Add cilantro if using.
Brush one side of all 4 tortillas with olive oil. Place 2 tortillas oil side down on a baking sheet. Place filling on top of each tortilla. Sprinkle 1 cup of cheese on top of each and top with remaining tortillas, oil side up.
Bake for about 10 minutes, turning once until cheese is melted and tortillas are a little brown.