This vegan recipe is perfect for using up leftover vegetables and can be a side or main dish. This recipe shows you how to make homemade ratatouille with thin slices of eggplant, zucchini, yellow squash, onion, Roma tomatoes drizzled with olive oil and served over seasoned tomato sauce. If you have potatoes, sweet potatoes, red and green peppers, beets, carrots, leeks, or mushrooms they are all great additions! Serve with pasta or a side of crusty bread.