In a mixing bowl, combine flour, sugar, and yeast. Add warm water, milk, and vegetable oil. Mix until a dough forms.
Knead the dough on a floured surface for about 10 minutes until smooth. Place in a greased bowl, cover, and let rise for 1 hour.
For the filling, combine ground pork, soy sauce, oyster sauce, sesame oil, sugar, garlic, ginger, and green onions in a bowl. Mix well.
After the dough has risen, punch it down and divide it into 12 pieces. Roll each piece into a ball and flatten into a disk.
Place a spoonful of filling in the center of each disk. Gather the edges and pinch to seal. Place each bun on a piece of parchment paper.
Steam the buns for 15-20 minutes until they are puffy and cooked through. Serve warm.