Combine the flour, yeast, sugar, salt and approximately 250 ml lukewarm water and knead to a dough. Cover and put to rise in a warm place away from draughts for about 1 hour. Then knead the dough again and leave to rise for a further 30-40 minutes.
Line a baking tray with baking parchment. Dust a work surface generously with flour and divide the dough into 12 balls. Roll each ball out to a circle with a rolling pin. Place on the baking tray and flatten evenly with your hands, leaving the dough a little thicker at the edge.
Brush the dough with a little olive oil. Wash and slice the tomatoes, removing the hard core at the top, and arrange on the pizzas. Sprinkle with cheese and bake in a preheated oven (220°C with top and bottom heat) for 8-12 minutes, until golden brown.
Meanwhile fry the prawns briefly in oil and season to taste with salt, pepper and lemon juice. Wash and sort the herbs, shake dry and sprinkle lightly with salt.
Put the mini-pizzas on a platter, top with prawns and herbs and serve.