In a blender container or food processor bowl, combine onion, peppers, garlic, lime juice, honey, mustard, ginger, salt, and pepper. Cover and blend or process until nearly smooth, stopping to scrape sides, if necessary. Set aside. Trim fat from meat. Cut 1/2-inch slits all over in meat at 1-inch intervals. Line a shallow roasting pan with a double thickness of heavy foil. Place meat, fat side up, on a rack in prepared pan. Spoon pureed mixture over meat, rubbing the mixture into the meat. Drizzle with melted margarine or butter.

Roast, uncovered, in a 325 degree F oven for 2 hours or until of desired doneness. Cover loosely; let stand 15 minutes before carving. Makes 10 to 12 servings.

Prepare onion mixture; cover and chill up to 24 hours before rubbing it over the lamb.