Defrost the prawns. Bring a large pan of water to the boil for the pasta. Add salt and a tablespoon of olive oil (it stops the pasta from sticking).
While the water is heating, peel and thinly slice the garlic. Place two tablespoons of olive oil in a large frying pan on a high heat, add the garlic and stir. Add the defrosted prawns, the frozen peas and a couple of tablespoons of hot water from the pasta pan
Add the butter, and salt and freshly ground pepper to taste. When the 'liquid' comes to a slight simmer and the shrimp start to turn pink/red, remove the pan from the heat.
Meanwhile, cook the capellini (or other pasta) according to the directions on the packet. Drain when cooked and drizzle about 3 tablespoons of olive oil over the top. Place in a large serving bowl and, using a slotted spoon, add the prawn and peas mixture from the frying pan. Stir well. Test for seasoning and add a little salt and freshly ground pepper if required. Serve onto individual plates and sprinkle with mint leaves, roughly chopped.