Mix honey, garlic, rosemary, mustard, lemon zest, and pepper together in a small bowl. Place lamb in a flat dish; rub mixture over lamb. Cover with plastic wrap and marinate in the refrigerator 8 hours to overnight.

Preheat the oven to 450 degrees F (230 degrees C). Transfer lamb onto a rack in a roasting pan and sprinkle with salt to taste.

Bake in the preheated oven for 20 minutes, then reduce heat to 400 degrees F (200 degrees C) and roast for 55 to 60 more minutes for medium rare. An instant-read thermometer inserted into the center should read at least 120 degrees F (50 degrees C). Let lamb rest for about 10 minutes before carving.