Combine shar siu, onions, oil, sugar, nam yue and five spice. Set aside. Dissolve yeast in warm water. Stir in biscuit mix. Turn onto floured pastry cloth and knead until smooth (about 20 times). Divide dough into 12 pieces. Grease hands and board with vegetable oil. Flatten pieces of dough into circles about 1/3" thick. Let the circles rest. Place 1/12 th of the filling on top of each circle. Form into buns by pulling the dough up around the filling. Pinch to seal the seams. Place on squares of waxed paper, smooth side up. Arrange on a steaming rack. Cover and let rise until doubled.