Preheat your oven to 400°F (200°C). Line baking sheets with parchment paper or grease with olive oil.

Wash and slice the eggplants. Sprinkle with salt and let sit on paper towels for 15 minutes.

Arrange eggplant slices on baking sheets. Drizzle with olive oil, season with salt and pepper, and roast for 20–25 minutes.

Heat olive oil in a skillet over medium heat. Cook the chopped onion for about 5 minutes, add garlic, then mushrooms, sauté for 8–10 minutes and season.

In a bowl, mix ricotta cheese, egg, Parmesan (if using), and parsley until smooth.

Reduce oven temperature to 375°F (190°C).

Spread a layer of marinara sauce at the bottom of a baking dish. Layer half of the roasted eggplant on top.

Add half of the ricotta mixture, half of the mushroom filling, another marinara layer, and half of the mozzarella cheese. Repeat layers and end with marinara and mozzarella.

Cover with foil and bake for 30 minutes. Then remove foil and bake for an additional 10–15 minutes until cheese is bubbly and golden.

Let rest for 10 minutes before slicing. Garnish with fresh basil and serve warm.