Heat the olive oil in a large pan. Add the onion and saute them on medium heat for about 4 minutes, then add the ground beef, and garlic to the pan, and continue to saute for about 8 minutes. After the ground beef turns brown, add the remaining ingredients to the pan. Cook for a few minutes until it boils; turn off the heat, and set it aside.
Peel the eggplants to form thick lines. Cut them into 0.5 cm/¼ inches discs. Heat the frying oil in a large pan. Fry the eggplant discs until they are soft and slightly golden brown on both sides, for about 2-3 minutes for each side.
Transfer the fried eggplant discs to the baking tray. Pour the ground beef mixture on top of the fried eggplant discs.
Bake it in the preheated oven at 190°C/375°F for about 45 minutes. Take the moussaka out of the oven, then transfer it to the serving plate.
Serve warm or hot. You can sprinkle chopped parsley on top before serving.