Preheat the oven to 450oF. Make sure your oven rack is at the centre.
In a large bowl, add bread crumbs, rosemary, salt, and pepper. Add some olive oil and toss all these ingredients together. Keep it aside.
Sprinkle the whole rack with salt and pepper correctly and over the high heat. Heat olive oil in a large ovenproof skillet.
Sear that rack of lamb for about 1-2 minutes from all sides and keep it aside for a few minutes.
Apply mustard to the lamb and cover it entirely with bread crumbs such that no area should be left uncovered. To prevent the charring of bones from ending, cover it with foil.
Keep the rack bone towards the downside in the skillet. Cook or roast the lamb for about 12-18 minutes in the oven. Cook the meat according to your taste and check if it needs to be cooked more or not. Monitor its temperature by taking it out.
Once done, let it rest for about 8 minutes, keep it covered, and then serve it.