Place lamb in a large bowl and coat with Greek Dressing. Cover and refrigerate at least 8 hours, preferably overnight.
Remove lamb from fridge about 1 hour before cooking to bring to room temperature. Scrape excess marinade from lamb, then sprinkle with Sea Salt and Black Pepper.
Preheat barbecue to medium-high. Place lamb, fat-side down, on grill. Grill for 2 minutes, then turn over and continue to grill for 2 more minutes.
Reduce heat to medium. Grill, turning occasionally, 18–20 more minutes for medium-rare. To check for doneness, insert an instant-read thermometer into thickest part of meat. It should read 145° F (63° C). Let stand 5 minutes before slicing.