Prepare rice in boiling salted water according to package instructions. Wash parsley, shake dry, pluck leaves from the stalks and chop. Clean and wash the aubergine, cut off a lid lengthwise.
Slightly hollow out the aubergine and season with salt and pepper. Cut the lid into cubes. Drain rice. Mix rice, eggplant cubes, parsley and cheese and fill eggplant with it. Cook in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for about 15 minutes.
In the meantime peel and dice the onion. Heat oil in a coated pan and sauté onion until translucent. Add the tomatoes and chop roughly. Season to taste with salt, pepper and sugar.
Arrange sauce and eggplant on a plate. Garnish with parsley and parmesan.