In a mixing bowl, combine flour, yeast, sugar, and baking powder. Gradually add warm water and knead until a smooth dough forms.

Cover the dough with a damp cloth and let it rise in a warm place for about 30 minutes.

Heat vegetable oil in a pan over medium heat. Add garlic and ginger, saut? until fragrant.

Add diced eggplant and cook until softened, about 5-7 minutes.

Stir in hoisin sauce, soy sauce, and sesame oil. Cook for another 2-3 minutes until well combined. Remove from heat and stir in scallions.

Divide the dough into equal portions and roll each into a circle. Place a spoonful of filling in the center.

Fold the dough over the filling and pinch to seal. Place each bao on a piece of parchment paper.

Bring water to a boil in a steamer. Place the bao in the steamer basket, cover, and steam for 10-12 minutes until fluffy.