Boil up plenty of salted water. Meanwhile peel and finely chop the garlic. Clean the chilli pepper, carve lengthwise, remove seeds, wash and chop finely. Wash parsley and cut into strips.
Cook the spaghetti in boiling water for about 10 minutes until al dente. Peel prawns, except for the tail fin, and remove the dark intestine. Wash the shrimps and dab them dry.
Heat 3 tablespoons of oil in a frying pan. Fry the prawns for 2-3 minutes. Add the rest of the oil, garlic and chilli. Fry for another 1-2 minutes. Add 5-6 tablespoons of the pasta water and bring to the boil.
Drain the spaghetti and put it back into the pot. Add the prawns and oil and mix well. Season to taste with salt, pepper and lemon juice. Arrange spaghetti in bowls or plates.