Heat a large skillet over medium high heat. Add olive oil, corn, garlic and chiles. Saute 3 minutes. Add zucchini, yellow squash and onions. Season with salt and pepper, chili powder; cook 7 to 8 minutes. Add stewed tomatoes and heat through. Transfer to baking dish. Cut 1 tube of polenta in 1/2" slices lengthwise. Top vegetables with polenta and cheese. Place in hot oven to melt cheese and warm polenta, 8 to 10 minutes. Garnish with chopped scallions and cilantro or flat leaf parsley.