Preheat oven to 400°F (200°C).

Brush the eggplant slices with olive oil and arrange them on a baking sheet.

Roast for 20 minutes, turning once halfway through.

Meanwhile, heat olive oil in a skillet over medium heat.

Cook the onion until softened, then add the garlic and mushrooms.

Stir in the tomato sauce, oregano, cinnamon, salt, and black pepper. Simmer for 10 minutes.

For the béchamel, melt the butter in a saucepan, whisk in the flour, then gradually add the milk until smooth and thickened. Stir in the Parmesan, nutmeg, and beaten egg if using.

In a greased baking dish, layer half of the roasted eggplant, followed by the tomato mixture. Repeat with the remaining eggplant and sauce.

Spread the béchamel evenly over the top.

Bake for 30 minutes until golden brown. Let rest for 10 minutes, garnish with fresh parsley, and serve warm.