Bao Bun with mushroom filling

Name: Bao Bun with mushroom filling
Ingredients: 1/3 cup warm water; 1/3 cup warm milk; 1 tbsp instant dry yeast; 2 tbsp sugar; 2 tbsp oil; 2 cups all-purpose flour; 1/2 cup corn flour; 1/2 teaspoon baking powder; 1 teaspoon salt; 200 gram mushroom; 1 onion; 1 capsicum; 1 tbsp oil; 1 tbsp butter; 1 teaspoon garlic paste; 1 teaspoon ginger paste; 1 teaspoon green chilli paste; 1/2 teaspoon black pepper powder; to taste salt; 1 tbsp Soya sauce; 1 tbsp chilli sauce; 2 tbsp coriander or spring onion