Trim fat from meat. Cut a pocket in the side of each lamb rib or loin chop; set aside.
Crush peppercorns with a mortar and pestle. (Or, place in a plastic bag; seal and crush peppercorns with the flat side of a meat mallet.) In a small bowl combine crushed peppercorns, mustard, rosemary, and garlic. Spread about 1/2 teaspoon of the mixture in the pocket of each chop. Reserve remaining mustard mixture.
Place lamb chops on the unheated rack of a broiler pan. Broil 3 to 4 inches from heat for 5 minutes.
Meanwhile, stir bread crumbs into remaining mustard mixture. Turn chops. Broil 2 minutes more. Spread some of the crumb mixture evenly over each chop. Broil for 3 to 4 minutes more for medium (160 degrees F) doneness. Garnish with rosemary sprigs, if desired. Makes 6 servings.