Mix the olive oil with the lemon juice, garlic and thyme. Pour this over the prawns, chill and marinate for 30 minutes.
Soak wooden skewers in water for about 30 minutes (if used).
Heat a barbecue or grill or a griddle pan. Thread the prawns carefully onto the skewers.
Cook on both sides for 2-3 minutes - until the prawns change colour to pink.
Seed the tomatoes, then chop finely. Mix with the oil, lemon juice, pepper and mint, then crumble the feta on top..
Serve the prawns with the feta & tomato relish scattered over them.