Combine first 4 ingredients in a small bowl.
Cut about 16 slits (about 1/2" deep) into lamb; insert garlic slices and a small amount of seasoned oil into each slit. Rub remaining oil over entire surface of lamb.
Place lamb on a rack in a roasting pan. Insert a meat thermometer into thickest part of roast, making sure it does not touch bone or fat.
Bake at 500° for 20 minutes; reduce temperature to 300°, and bake 1 hour and 10 minutes or until thermometer registers 150° (medium rare) or 160° (medium). Let stand 10 minutes. Slice lamb diagonally across the grain. Serve with Pineapple-Pecan Salsa.