We have been having an abundance of Basil, one of my favorite herbs.  This was such an easy, simple dish where Basil is the highlight.  Some of the ingredients, I just eye-balled - or judge to taste.  A great summer side dish for any main meal.
1 large Beefsteak tomato, sliced in quarter inch pieces
1 medium zucchini, sliced into quarter inch pieces - about 22 slices
1 large handful of fresh Basil
1/4 cup roughly sliced red onion
Olive Oil
Balsamic Vinegar
1/2 cup Parmesan Cheese
1 cup grated Swiss Gruyere Cheese
salt and pepper
Drizzle some olive oil into a gratin pan or casserole dish - swirling to coat.  Lay down the zucchini slices, spreading the sliced red onion throughout.  Roughly tear up the basil, sprinkling on top of the red onion.  Season with salt and pepper.
Lay the tomato slices on top, season with salt and pepper, then drizzle Balsamic Vinegar throughout - eye ball or to taste.
Sprinkle the Parmesan cheese on top, then scatter the grated Swiss Gruyere Cheese evenly.  Cover and bake in a 350 degree oven for 20 minutes, then remove the lid and continue to bake for another 10 minutes.  Serve hot with any main dish.