Combine first 7 ingredients in a bowl and let stand 2 minutes. Slowly whisk in both oils in thin stream. Cover and let stand 1 day.
Place lamb in shallow baking dish. Whisk marinade, then pour over lamb; turn to coat both sides. Let stand at room temperature 2 hours or chill overnight, turning occassionally.
Prepare grill (high heat) or preheat broiler. Arrange lamb on grill. Barbecue about 4 minutes per side for medium-rare. Transfer lamb to platter. Brush with marinade and garnish with mint. Serve immediately, passing jalapeno jelly seperately.