Preheat your oven to 400°F (200°C) and line a baking sheet with parchment paper.
Slice the eggplant into 1/2-inch thick rounds. Lightly brush both sides with olive oil and sprinkle with a pinch of sea salt.
Roast the eggplant slices for 15-18 minutes until softened and slightly browned, then remove from the oven.
While eggplant roasts, heat a non-stick skillet over medium heat. Add the ground lamb, diced onion, and minced garlic.
Sauté the lamb mixture until the meat is browned and the onions are translucent, draining any excess fat if necessary.
Stir in the tomato puree, dried oregano, ground cinnamon, sea salt, and black pepper. Simmer on low for 5-7 minutes to meld flavors.
In a small mixing bowl, whisk together the Greek yogurt and egg white until completely smooth and combined.
In a small oven-safe baking dish, place a layer of roasted eggplant slices, followed by the lamb mixture, and then the remaining eggplant slices.
Pour the yogurt mixture evenly over the top layer of eggplant and sprinkle with the crumbled feta cheese.
Bake for 20-25 minutes until the topping is set and develops a light golden-brown color. Let rest for 5 minutes before serving.