Sprinkle prawns with salt and pepper. Heat olive oil, chilli flakes and garlic in a nonstick frypan and cook until fragrant, about 3 minutes. Add prawns to frypan and cook until just done, about 2 minutes. Stir in lemon juice and take off the heat.
Place tomatoes in a salad bowl and sprinkle lightly with salt. Add toasted bread, prawns and basil leaves and toss gently.