Preheat the oven to 200°C. Grease a baking sheet with cooking oil and set it aside.
Rinse prawns under cool running water and dry them off using a clean kitchen towel.
To butterfly tiger prawns pull down the prawns’ tails until they break. Using a paring knife, cut the back of each prawn from its head to its tail through the middle of its body and along the inside curve of the top shell; open like a book.
Then pull off and discard shells, devein and wash prawns with cold running water. Pat dry with paper towels or leave to drain for several minutes before roasting in butter.
In another bowl mix garlic, lemon juice, softened butter and herbs together using a spoon or hand blender until well combined. Season to taste with salt and pepper. Set aside.
Place prawns on the prepared baking sheet, with the head facing down and the tail facing up.
Gently brush the garlic butter over the prawns in an even distribution.
Transfer the pan to the oven and roast for 7-8 minutes or until cooked through.
Serving Suggestions: Serve immediately, sprinkled with parsley and lemon wedges on the side.