Preheat oven to 350°F. Melt 1 tablespoon butter in heavy large skillet over medium-high heat. Add zucchini and onion and sauté until vegetables are just tender, about 4 minutes. Mix in 1 cup corn, canned chilies and 1/4 cup cilantro; season filling with salt and pepper.
Melt 3 tablespoons butter in heavy medium saucepan over medium-high heat. Whisk in chili powder, flour and cumin; stir 30 seconds. Gradually whisk in milk. Cook until sauce is thick and bubbling, whisking occasionally, about 5 minutes. Add 1 1/2 cups cheese; whisk until smooth. Season with salt and pepper.
Spread 1/4 cup sauce in bottom of 13 x 9 x 2-inch glass baking dish. Mix 3/4 cup sauce into filling. Place generous 1/3 cup filling in center of 1 tortilla; roll up to enclose filling. Place enchilada in baking dish. Repeat with remaining tortillas and filling. Cover enchiladas with remaining sauce, then sprinkle with remaining 1/2 cup corn and 1/2 cup cheese.
Bake vegetable enchiladas until heated through, about 45 minutes. Sprinkle with 1/4 cup cilantro and serve.
