Preheat oven to 425 degrees F.
Combine tomatoes, 1 cup onion, garlic, chile, chili powder, oregano, cumin and salt in a blender; puree on high until smooth, about 1 minute.
Spread ½ cup of the sauce in a 9-by-13-inch baking dish. Layer 4 tortillas over the sauce. Top with ½ cup zucchini, ½ cup corn, ½ cup cheese and ¼ cup of the remaining onion. Repeat the layers twice. Top with the remaining tortillas, zucchini, corn and onion. Spread the remaining sauce on top.
Coat a large piece of foil with cooking spray and cover the baking dish tightly. Bake the enchiladas for 10 minutes. Remove the foil and sprinkle on the remaining ½ cup cheese. Continue baking until the cheese is melted and the edges are starting to brown, 15 to 20 minutes longer.
