To make the mint salt, place the Vietnamese mint and salt in the bowl of a small food processor and process until well combined. Set aside.
Heat a char-grill pan or barbecue over high heat. Toss prawns with half of the oil and char-grill or barbecue for 1–2 minutes each side or until cooked through. Set aside and keep warm. Toss the snow peas with the remaining oil and char-grill or barbecue for 1–2 minutes or until just tender. Serve with the prawns, lemon wedges and mint salt. Serves 4.