Slice eggplant, zucchini, tomato, bell pepper, and onion thinly.
Heat olive oil in a pan and sauté onion and garlic.
Add the remaining vegetables, season with salt and pepper, and stir-fry.
When the vegetables are soft, add basil and mix well.
Cut ciabatta bread in half and toast.
Spread the ratatouille vegetables on the bread and add your desired amount of cheese.
Cover with the other half of bread to finish the sandwich.