Preheat your oven to 400°F and line a baking sheet with parchment paper.
Slice the eggplant into half-inch rounds, brush lightly with olive oil, and roast for 15 minutes until tender and slightly browned.
While eggplant roasts, sauté the diced onion and minced garlic in a non-stick skillet over medium heat until translucent.
Add the ground lamb to the skillet, breaking it up with a wooden spoon and browning it thoroughly until no pink remains.
Stir in the tomato puree, cinnamon, oregano, sea salt, and black pepper, then let the mixture simmer for 5 minutes to develop the flavors.
In a small bowl, whisk together the Greek yogurt and the egg until the mixture is smooth and well combined.
In a small oven-safe baking dish, layer half of the roasted eggplant slices, then spread the lamb mixture evenly over them.
Place the remaining eggplant slices on top of the lamb and pour the yogurt-egg mixture over the entire dish.
Bake for 20-25 minutes until the topping is set and has turned a beautiful golden-brown color.