"Frenched" racks of lamb have had the rib bones scraped clean.
Preheat grill to medium. Meanwhile, stir together pepper, salt, and red-pepper flakes. Rub lamb with olive oil and 1/4 cup pepper mixture. Let stand 15 minutes.
Brush hot grill with vegetable oil. Grill lamb, turning occasionally, until a thermometer inserted into thickest part of flesh (do not touch bone) reaches 125 degrees for medium-rare, about 25 minutes.
Transfer lamb to a cutting board; let rest at least 15 minutes and up to 30 minutes. Slice into chops and serve with jam and remaining pepper mixture.