Pour onion mixture in the bottom of a 2 quart oiled baking dish and sprinkle with chopped basil.
Make rows of alternating zucchini, summer squash, and tomato standing them almost on end.
Sprinkle top with sea salt & fresh cracked pepper, Parmesan cheese, and toasted bread crumbs.
Drizzle with olive oil.
Bake 20 - 25 minutes until veggies are tender.
Let stand at least 5 minutes before serving.
Notes
You can definitely make this dish ahead, just wait to add the Parmesan and bread crumbs until just before baking. The fresh herbs really make this dish.