Preheat oven to 450° F. Then, in a medium roasting pan or Dutch oven, place boneless leg of lamb roast and make 20-30 inserts with a paring knife. Stick garlic slice into each opening until you run out of garlic.
Bake uncovered until desired doneness. Remember meat will keep "cooking" as it rests. My best advice for 4-5 lbs roast is to check internal temperature after 1 hour and go from there. For 2-3 lbs roast, check after 45 minutes.
Refrigerate roast whole or sliced in an airtight container for up to 5 days. It tastes so good cold or freeze leftovers sliced or cut into bite sized pieces in an airtight container for up to 3 months. Thaw in the refrigerator.