Pour water into a large pan. Add a good pinch of salt and place over a high heat.
Bring to the boil.
Cook the spaghetti according to the instructions.
Over a medium heat, add the oil to a frying pan. When hot, add the garlic and chilli until softened.
Add the chopped tomatoes, vinegar and sugar and bring to a gentle simmer.
Simmer for 5 minutes.
When the pasta is cooked, place a colander over a mug and drain the pasta. The mug is to catch some of the pasta water.
Add the drained pasta and the prawns to the tomato sauce and a few spoonful's of the pasta water. The pasta water is used to loosen the sauce so it covers the spaghetti well.
Toss everything together well and serve immediately.