Preheat oven to 450°F.

Heat 3 tablespoons of olive oil in a skillet over medium heat.

Add chopped garlic and onion to the skillet and cook until aromatic and beginning to brown.

Add stewed tomatoes and 1 tablespoon of dried oregano to the skillet.

Once tomatoes begin to bubble, stir in tomato paste.

Reduce heat to low, add salt and pepper to taste, cover and let simmer lightly while you continue.

Slice eggplant lengthwise into 1/4-inch slices.

Spread out eggplant slices on a rimmed cookie sheet sprayed lightly with nonstick cooking spray.

Salt the slices generously on both sides, sprinkle with thyme, and lightly brush with the remaining olive oil.

Roast eggplant in oven until tender and slightly browned.

If using yellow squash, also roast briefly until soft and pliable.

Remove and let cool enough to handle.

Reduce oven to 375°F.

Meanwhile, stir together ricotta cheese, egg, remaining oregano, and 1/4 cup of Parmesan cheese in a bowl.

In a 12x9-inch baking dish spread 1/4 cup of tomato sauce.

Cover with 3 or 4 eggplant slices, then half of the roasted peppers, and then a third of the ricotta cheese mixture.

Followed by a third of the mozzarella.

Sprinkle half the basil over cheeses, and then spinach and yellow squash (if using).

Cover with more tomato sauce, eggplant, peppers, ricotta, mozzarella and basil.

Top with remaining eggplant, tomato sauce, mozzarella, and any remaining Parmesan.

Cover with foil and bake for about 15 minutes.

Remove foil and bake for about 15 minutes more or until cheese is bubbly and beginning to brown.

Remove and let cool for at least 5 minutes before serving.