Summer Veggie Au Gratin

This is a dish I have been making for years. It's gone through several transformations and been given just as many names. But when I really think of it, it clearly is an Au Gratin that's FULL of beautiful Summer vegetables. So I'm thinking the name fits! And the flavor combination is amazing! The slightly caramelized onion and Parmesan really pull it all together. Served piping hot with some garlic bread and grilled meat of choice, it really dresses up your dinner. Enjoy!

Ingredients:
4 Tbsp extra virgin olive oil, divided
1 large sweet onion, sliced into rings
2 Roma tomatoes, thinly sliced
2 small zucchini, thinly sliced
2 small yellow squash, thinly sliced
2 cloves garlic, minced
dash of salt and pepper
1 cup  Parmesan cheese plus another 1/2 cup for garnish (1 1/2 cups total)
3/4 cups panko bread crumbs

Directions:
Pre-heat oven to 400 degrees. Toss your zucchini and squash with 2 Tbs olive oil, 2 cloves of minced garlic, salt and pepper, in a medium mixing bowl; set aside. Freshly grate 1 1/2 cup of Parmesan. (The green can of sprinkle cheese does NOT work well with this dish.) Place cheese in a small mixing bowl and combine with panko bread crumbs. Set it aside as well. Drizzle the other 2 Tbs olive oil on to the center of a rimmed cookie sheet. Lay your sliced onions on top of the oil. (Kind of swoosh them around to make sure the entire bottom of dish is lightly coated with oil.) Layer your sliced tomatoes on top of the onions. Top with zucchini and squash slices. Sprinkle with panko/Parmesan mix and top with additional 1/2 cup of Parm. Bake UNCOVERED for about 20 minutes. Just until topping is lightly browned and onions start to caramelize. (I like to leave some of the edges of my onions showing so I can tell when they're done.)