Peel and slice the garlic. Peel the king prawns, leaving the heads and tails intact, then run a small sharp knife down the back of each to butterfly it, also removing the vein.
Place the prawns in a non-stick frying pan on a medium-high heat with 2 tablespoons of olive oil and cook for 3 to 4 minutes, or until the prawns are just cooked, shaking the pan constantly and adding the garlic and the leaves from a few sprigs of oregano for the final minute.