Preheat your oven to 400°F.
Cut the eggplant into 1-inch cubes. Toss with olive oil, a pinch of salt, and pepper, then spread evenly on a baking sheet.
Roast the eggplant in the preheated oven for about 20 minutes, or until it is tender and lightly browned.
While the eggplant roasts, heat a non-stick skillet over medium heat. Sauté the sliced onion in a little olive oil until softened, about 3-4 minutes.
Add the minced garlic and cook for an additional 1 minute until fragrant.
Add the lean ground beef to the skillet, breaking it up with a spoon. Cook until the beef is browned and cooked through, about 5-7 minutes. Drain any excess fat if necessary.
Remove the skillet from heat and stir in the non-fat Greek yogurt until the mixture achieves a creamy consistency. Season with salt and pepper to taste.
Gently fold in the roasted eggplant, allowing the flavors to meld together.
Transfer the mixture into an oven-safe baking dish. Sprinkle the part-skim mozzarella evenly over the top.
Place the dish back in the oven for 5-7 minutes or until the cheese is melted and bubbly.
Remove from the oven, let it cool slightly, and serve warm enjoying the creamy, savory flavors of the roast.