Preheat your oven to 400°F and line a baking sheet with parchment paper.
Slice the eggplant into half-inch thick rounds and arrange them on the prepared baking sheet, roasting for 20 minutes until tender.
While the eggplant roasts, place a skillet over medium heat and brown the ground lamb with the diced yellow onion and minced garlic until the meat is cooked through.
Stir the tomato puree, ground cinnamon, dried oregano, sea salt, and black pepper into the lamb mixture and let it simmer for 5 minutes to meld the flavors.
In a small mixing bowl, whisk together the non-fat Greek yogurt, egg, and ground nutmeg until the custard is completely smooth.
In a small oven-safe baking dish, layer half of the roasted eggplant slices, followed by the lamb mixture, and then the remaining eggplant slices.
Pour the yogurt custard over the top, spreading it evenly, and bake at 375°F for 20 minutes until the topping is set and beautifully golden.