Heat a large saucepan, spray it with the oil, add the prawns and garlic and season to taste. Cover tightly and cook, shaking the pan from time to time, for about 3 minutes or until the prawns are cooked.
Add the tomatoes, rocket, spinach and watercress and stir until wilted. Squeeze over the lemon juice and check the seasoning.
Serve immediately, with French bread if liked.