Make 1-inch-deep cuts in lamb, and insert garlic slices. Place lamb in a shallow roasting pan.
Bake at 325° for 1 hour.
Stir together honey and next 3 ingredients in a small saucepan; cook over low heat until bubbly, stirring until sugar dissolves. Remove from heat, and stir in lemon rind, mint, and walnuts.
Spoon lemon glaze over lamb; bake 30 more minutes or until a meat thermometer inserted into thickest portion registers 155° or to desired degree of doneness, basting occasionally with glaze. Serve lamb immediately.