Cut five slits in the meat; insert garlic. Combine salt, pepper, thyme and garlic powder; rub over meat. Place on a rack in a roasting pan. Broil 5-6 in. from the heat until browned; turn and brown the other side. Turn oven to 350°. Add 1/2 cup water to pan. Cover and bake for 25 minutes per pound or until internal temperature reaches 140° for medium or 145° for medium-well. Remove to carving board and keep warm. Pour pan drippings into a large measuring cup, scraping brown bits. Skim fat; reserving 1/4 cup in a saucepan; add flour. Add water to drippings to equals 2 cups; add all at once to flour mixture. Bring to a boil; cook and stir until thickened and bubbly. Cook and stir 1-2 minutes more. Slice lamb and serve with gravy.