Peel the prawns. To devein them, make a shallow cut along the back of each prawn and remove the black vein.
Pour the olive oil into a large non-stick frying pan and heat over a medium heat. Add the garlic and cook briefly until tender, making sure it does not burn.
Add the prawns and cook, stirring frequently, for about 3 minutes. Add the stock, lemon juice and chilli flakes and bring to the boil. Cook for about 1 minute or until the prawns are opaque.
With a slotted spoon, transfer the prawns to serving plates. Bring the liquid in the pan to the boil, stir in the cornflour mixture and cook, stirring, for about 1 minute or until the sauce is lightly thickened. Stir in the parsley and spoon the sauce over the prawns.