Preheat oven to 400°F (200°C).
Slice eggplant into 1/2-inch rounds, brush with olive oil, and roast on a baking sheet for 15 minutes until softened.
In a skillet over medium heat, sauté finely chopped onion, minced garlic, and ground lamb until the meat is fully browned.
Stir in the tomato sauce, cinnamon, oregano, sea salt, and black pepper, allowing the mixture to simmer for 5 minutes.
In a small bowl, whisk together the Greek yogurt, egg, and parmesan cheese until smooth.
In a small oven-safe baking dish, layer half the eggplant, all of the lamb mixture, the remaining eggplant, and finally the yogurt topping.
Bake for 20-25 minutes until the custard topping is set and develops a beautiful golden-brown color.