1.Preheat oven to 200°C/180°C fan-forced.
2.Make mustard maple glaze by combining the butter, maple syrup and mustard in a small saucepan over low heat. Cook, stirring, until slightly thickened.
3.Meanwhile, using sharp knife, make cuts in lamb; press garlic slices into cuts. Place lamb in large oiled baking dish; brush with 2 tablespoons of the glaze.
4.Combine remaining glaze, parsnip and kumara in medium bowl.
5.Place vegetables in baking dish with lamb; roast, uncovered, about 15 minutes or until vegetables are tender and lamb is cooked as desired. Stir parsley into vegetables; serve with lamb.