Prepare rice according to package directions.
Cook zucchini, onion and corn in a skillet over medium heat, with butter and and olive oil until soft and beginning to brown, about 10 minutes.
Place cooked rice in a large casserole and mix with soup and sour cream.
Stir in vegetables and half of cheese. Smooth out top and sprinkle with remaining cheese.
Refrigerate up to 24 hours.
Bake uncovered at 350 for 45-60 minutes until heated through. Serves 6-8