Inspired by the classic French dish, this ratatouille casserole is a medley of flavors and textures. Made with a combination of eggplant, zucchini, bell peppers, tomatoes, and onions, this casserole is a celebration of summer vegetables. The vegetables are sautéed until tender and then baked with a tomato-based sauce, allowing the flavors to meld together. Serve it as a main course or as a side dish with crusty bread.