To prepare a baby vidalia onion pie main dish recipe, you'll first need to prepare your ingredients. First, peel and cut the baby Vidalia onions. Then, slice the onion lengthwise, then cut it in half. Cut each half into 8 slices. Place the slices of onion in the bottom of an oven-proof pie dish. Pour the tomato sauce over the onions, and bake the pie for 20 minutes. Remove the pan from the oven and sprinkle with the Parmesan cheese. Serve warm.