Preheat oven to 450 degrees F.

Mix breadcrumbs, 1/2 teaspoon oil, 1/2 teaspoon rosemary, 1/2 teaspoon salt and 1/8 teaspoon pepper in a small bowl.

Heat the remaining 1 teaspoon oil in a large ovenproof skillet over medium-high heat. Add lamb, meat-side down, and sear until browned, about 1 1/2 minutes. Turn it over and spread 2 teaspoons mustard over the meat. Sprinkle the breadcrumb mixture over the mustard. Transfer the lamb to the oven and roast until a thermometer inserted in the center registers 140 degrees F for medium-rare, 15 to 20 minutes. Transfer to a plate and tent with foil to keep warm.

Return the pan to medium-high heat (be careful: the handle will still be hot). Add shallots, the remaining 1/2 teaspoon rosemary, 1/4 teaspoon salt and 1/8 teaspoon pepper and cook, stirring constantly, until starting to soften, about 1 minute. Stir in lentils, apple, celery, broth (or water), vinegar and the remaining 1 teaspoon mustard; bring to a lively simmer. Cook, stirring occasionally, until the liquid is slightly reduced and the celery and apple are starting to soften, about 4 minutes. Cut the lamb into 8 chops and serve over the lentils.

Note: We like Ian's brand of coarse dry whole-wheat breadcrumbs, labeled "Panko breadcrumbs." Find them in the natural-foods section of large supermarkets. Or, make your own breadcrumbs: Trim crusts from firm sandwich bread. Tear the bread into pieces and process in a food processor until coarse crumbs form. One slice makes about 1/3 cup. Spread the breadcrumbs on a baking sheet and bake at 250 degrees F until dry and crispy, about 15 minutes.