Preheat oven to 375 degrees Fahrenheit. Place corn tortillas on baking sheets. Bake for 10 minutes or until crisp. Meanwhile, heat a large, nonstick pan over medium-high heat. Add oil. Once hot, sauté zucchini, tomatoes, onion, peppers, corn and scallion for 4 minutes. Drain excess liquids through a mesh strainer. Return vegetables to pan. Stir in cilantro and salt. Onto each of 4 baked tortillas, sprinkle 3 tablespoons of the cheese and 1/8 of vegetable mixture. Top each with another baked tortilla. Sprinkle with the remaining cheese and vegetable mixture. Top with remaining baked tortillas. Serve each "tower" with 1 tablespoon sour cream, and if desired, fresh cilantro.
Timesaving tip: Chop veggies in advance and refrigerate up to 3 days.