In a large, glass bowl, stir together the olive oil, lemon juice, parsley, garlic and black pepper. Season with chilli flakes, if desired. Add prawns, and toss to coat. Marinate in the refrigerator for 30 minutes.
Preheat barbecue for high heat. Thread prawns onto skewers, piercing once near the tail and once near the head. Discard any remaining marinade.
Lightly oil cooking grill hotplate. Cook for 2 to 3 minutes per side, or until opaque.