Preheat oven to high grill.
Slice bread into 12 pieces. Lay on lined oven tray and grill for 3 minutes each side, until lightly toasted. Watch bread carefully at this stage as it can burn easily.
Once bread has toasted slightly, layer on sauce. Top with torn mozzarella, place back in oven and grill for 2-3 minutes, or until mozzarella is melted.
Toss rocket in a small bowl with vinegar. Once cheese has melted, remove toast from oven and top with rocket. Season to taste.