Mix warm water, sugar, and yeast in a bowl
Let the yeast sit until foamy
Add flour, baking powder, and salt
Mix until a dough forms
Knead the dough until smooth and elastic
Cover the dough and let it rise until doubled in size
Punch down the dough
Divide the dough into equal pieces
Shape each piece into a smooth ball
Roll each ball into an oval
Brush lightly with oil
Fold each oval in half
Place each bun on parchment paper
Let the buns rise again until puffy
Steam the buns over boiling water until cooked through
Remove and serve warm