Combine first 6 ingredients in a medium saucepan; bring to a simmer over medium heat, stirring frequently. Reduce heat to low, and cook, uncovered, 12 minutes; set aside.
Combine zucchini, corn, 3/4 cup cheese, chips, and green chiles in a bowl; stir well. Spoon zucchini mixture into a 13 x 9-inch baking dish coated with cooking spray. Pour tomato sauce mixture over casserole; bake, uncovered, at 350° for 25 minutes. Sprinkle remaining cheese over casserole, and bake an additional 5 minutes.
Spread sour cream over casserole, and sprinkle with bell pepper and tomato.