Preheat oven to 400°F (200°C)
Cut each eggplant in half lengthwise. Using a knife, cut the flesh of each eggplant in a cross-hatch pattern; be careful not to cut through the skin. Place the eggplant halves on a baking tray, flesh side up. Drizzle with olive oil and season with salt and pepper. Then, bake for about 30 minutes until soft.
In the meantime, prepare the beef marinara sauce. Heat a dry, non-stick pan over medium-high heat and cook the ground beef for 5-6 minutes until browned. Add in the onion and garlic, and cook for another 3-4 minutes.
Next, add in the diced tomatoes, tomato paste, and rosemary, then bring to a boil. After bringing to a boil, reduce heat to low. Continue simmering until eggplant is ready, which should take around 20 minutes.
Remove the eggplant from the oven, and scoop out the centre, leaving enough meat inside the skin to hold its shape. Chop the removed flesh, and add to the beef, mixing well.
Spread ¼ of the beef marinara sauce over each eggplant half, and sprinkle each with cheese.
Place the stuffed eggplant back into the oven, and continue to cook for about 10 more minutes until lightly browned.