1. Pre-heat oven to 180°C.
2. To make herb crust, process olive oil, Ciabatta, lemon juice, zest, garlic and herbs in a food processor until finely chopped. Season with salt and pepper. Transfer to a bowl.
3. Place leg of lamb into an ovenproof dish. Pour 250ml water into the base of the ovenproof dish. Use a pastry brush to baste Vegemite all over the leg of lamb, ensuring the entire leg is covered. Press breadcrumb mixture onto lamb.
4. Roast racks of lamb for 20 minutes or until cooked to your liking.
5. Remove lamb from the oven and leave to rest for 10 minutes before serving.