1Combine soy sauce, sugar, sesame oil, vinegar, peanut butter, chili garlic sauce or chili paste, tahini or sesame paste, garlic and grapeseed oil in a large bowl; mix well. Add lamb and turn to coat. Let stand for 10 minutes, or cover and refrigerate for up to 4 hours.
2Remove meat from marinade. Place a grill pan over medium-high heat until hot; brush with oil. Place lamb chops in pan and cook, turning once, until medium-rare, about 6 minutes on each side.
3Pour marinade into a small saucepan. While lamb is cooking, place saucepan over medium-high heat and bring reserved marinade to a boil. Cook, stirring, for 1 minute.
4Pour reserved marinade over lamb and serve.