Preheat oven to 475°. Off the heat, mix first 5 ingredients in a small saucepan. Place tenderloin on a greased rack in a foil-lined 15x10x1-in. pan; brush with 1/4 cup hoisin mixture. Roast until a thermometer reads 145°, 15-20 minutes., Stir water into remaining hoisin mixture; bring to a boil. Reduce heat; simmer, uncovered, to allow flavors to blend, about 5 minutes, stirring occasionally. Remove from heat; stir in butter. Keep warm., Remove pork from oven; let stand 5 minutes before slicing. Cook noodles according to package directions, omitting seasoning packets; drain. Serve with pork; top with sauce and green onions.