Preheat your oven to 400°F and line a large baking sheet with parchment paper.
Slice the eggplant into 1/2-inch thick rounds and arrange them in a single layer on the prepared baking sheet.
Lightly brush the eggplant rounds with the olive oil and roast for 15 minutes until they are tender and slightly browned.
While the eggplant is roasting, finely dice the onion and mince the garlic.
Heat a non-stick skillet over medium heat and sauté the onion and garlic until translucent and fragrant.
Stir in the cooked lentils, tomato puree, cinnamon, oregano, sea salt, and black pepper, then simmer for 5 minutes to meld the flavors.
In a small mixing bowl, whisk together the Greek yogurt, egg, and nutritional yeast until the mixture is completely smooth.
In a small oven-safe baking dish, layer half of the roasted eggplant slices, followed by the spiced lentil mixture, and then the remaining eggplant.
Pour the yogurt and egg mixture over the top layer, using a spatula to spread it evenly to the edges of the dish.
Bake for 20-25 minutes until the topping is set and has developed a beautiful golden-brown hue.