In a large pan, heat 2 tablespoons of olive oil over medium heat. Add the prawns and fry for 3 minutes, stirring constantly. Then lift out the prawns with a slotted spoon.
In the same pan, heat the remaining 2 tablespoons of olive oil, add the spring onions and sauté for about 8 minutes until they are soft. Add the garlic and cayenne pepper and cook for another 2 minutes. Add the tomatoes and cook for about 2-3 minutes until the mixture is a little thicker. Add a pinch of sugar and season with salt and pepper.
Spread the sauce evenly over the prawns in a baking dish and crumble the feta cheese over it.
Bake in the oven until the cheese melts (5-8 min). Sprinkle with parsley and serve hot.