Preheat the Oven: Preheat your oven to 400°F (200°C). Line a large baking sheet with parchment paper.
Prep and Roast the Eggplant: Score the flesh of each eggplant half in a diagonal diamond pattern, being careful not to cut through the skin. Brush the cut sides generously with olive oil and season with salt and pepper. Place them cut-side up on the baking sheet and roast for 25 minutes, or until the flesh is soft and lightly golden.
Make the Filling: While the eggplants roast, heat olive oil in a large skillet over medium-high heat. Add the ground beef and cook, breaking it up with a spoon, until browned. Drain any excess fat.
Sauté Aromatics: Stir in the diced onion and garlic. Cook for 4 to 5 minutes until the onions are soft and translucent. Stir in the oregano, cumin, salt, and pepper.
Simmer Sauce: Pour in the crushed tomatoes. Lower the heat to medium-low and let the mixture simmer gently for 10 minutes, allowing the flavors to meld and the sauce to thicken.
Assemble the Boats: Remove the eggplants from the oven. Use the back of a spoon to gently press down the soft centers of each eggplant half, creating a hollow boat shape.
Fill and Bake: Divide the warm meat filling evenly among the four eggplant halves. Top each generously with the shredded mozzarella cheese. Return to the oven and bake for 10 to 12 minutes, or until the cheese is melted, bubbling, and golden brown.
Garnish and Serve: Remove from the oven. Garnish immediately with crumbled feta and chopped fresh parsley. Serve warm.