Vegetarian Times calls this a "light summer entree". I don't know if I would count on it being very filling, but it was perfect on the side of last night's Broccoli-Edamame Soup.
2 medium zucchini, cut into 1/8 thick slices
1 1/2 lb tomatoes, cut into 1/4 inch thick slices (I used romas)
4 cloves garlic, minced
2 Tbs chopped kalamata olives
1/4 C thinly sliced/chopped fresh basil
3/4 C grated Parmesan cheese
First, drape the tomato slices over a colander, sprinkle them with salt, and let them drain for about 45 minutes.
Next, spread out the zucchini slices on a cookie sheet or cutting board. Sprinkle them with salt and allow them to sit for about half an hour "sweating" their moisture out.
After half an hour, heat about a teaspoon olive oil in a large skillet over medium-high heat. Saute the zucchini for about four minutes until golden and beginning to soften - you may need to do this in two batches if your skillet isn't big enough.
Layer half of the zucchini into the bottom of an 8-inch square baking dish. Top with half of the tomatoes and sprinkle with half of the garlic, olives, and basil. Season with a bit of black pepper and sprinkle about 1/4 cup of Parmesan over the entire layer.
Repeat with the layering second half of the zucchini followed by the rest of the tomatoes, olives, garlic, and basil. Top it with all of the remaining cheese.
Bake at 375 covered with foil for ten minutes, then remove the foil and bake for 20 minutes more. You want the cheese to be "melty" and the gratin to be bubbly.
Let it stand for 5 to 10 minutes before serving.