Peel onion and garlic and cut into fine cubes. Wash parsley, shake dry, pluck leaves from the stalks and chop. Heat the oil. Sauté onion and garlic until translucent.
Add tomatoes and parsley, except for something to garnish. Chop the tomatoes with the spatula. Season with salt and pepper. Bring to the boil and simmer for 2-3 minutes. Peel the scampi, except for the tail fin, and remove the intestines.
Wash the scampi and pat them dry. Arrange the scampi and tomato sauce on 6 oven-proof plates. Crumble feta cheese and sprinkle over the scampi. Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: level 2) for about 10 minutes.
Sprinkle with the rest of the parsley.