If the shrimp/prawns you are using haven't been shelled, remove the head and shell and make sure the shrimp has been deveined. You can easily devein shrimp by cutting along the back of the shrimp and carefully remove the black vein (this is the shrimp's digestive tract and isn't edible). When using frozen shrimp, make sure they are fully thawed then pat them dry with paper towel and season with salt and pepper.
Melt the butter in a large frying pan over high heat.
Add the shrimp the pan in batches (to avoid over-crowding) and cook until the shrimp are cooked. Remove from the pan and set aside.
Add the garlic to the pan and allow to fry for a few seconds before adding back the shrimp. Add the lemon juice and parsley and cook for another minute.