Preheat oven to 400°F (200°C) and line a baking sheet with parchment paper.
Slice the eggplant in half lengthwise, score the flesh in a crosshatch pattern, and roast for 20 minutes until softened.
While eggplant roasts, brown the ground lamb in a large skillet over medium heat until no longer pink.
Add the diced onion and minced garlic to the skillet, sautéing for 5 minutes until the onion is translucent.
Stir in the tomato sauce, cumin, cinnamon, salt, and pepper, letting it simmer for 3 minutes to meld the flavors.
Carefully scoop out the center of the roasted eggplant halves, leaving a 1/2-inch border, and mix the flesh into the lamb mixture.
Spoon the lamb and eggplant mixture back into the shells and bake for an additional 10 minutes.
Serve warm with a dollop of Greek yogurt and a sprinkle of fresh parsley.