In a small bowl, combine the honey, mustard, rosemary, ground black pepper, lemon zest and garlic. Mix well and apply to the lamb. Cover and marinate in the fridge overnight.
Preheat the oven to 230 C.
Place lamb on a rack in a dish and sprinkle with salt to taste.
Bake in the preheated oven for 20 minutes, then reduce heat to 200 C and roast for 55 to 60 more minutes for medium rare. The internal temperature should be at least 63 degrees C. Let the roast rest for about 10 minutes before carving.