In a medium bowl, sift matcha powder, flour, and baking powder and mix. Set aside.
Warm the milk in a small bowl. Add yeast and 1 teaspoon of sugar and mix. Let the mixture sit for 10 minutes until it starts to foam to proof the yeast. Add vegetable oil and the rest of the sugar. Stir until combined.
Add the wet ingredients to the dry ingredients. Combine with your hands. Once all the ingredients come together, dump the dough onto a floured surface and knead (I used a kitchen aid with a dough hook in 2 minute increments). Add flour if the dough is too sticky. The dough has been kneaded enough if you poke the dough and it slowly springs back at you. Once done, transfer it to an oiled bowl and cover with a towel. Let it rise in a warm place (1-3 hours).
Once the dough is finished proofing, divide it into small equal pieces. Roll out each piece into a thin circle that is 3-4 inches in diameter. Add 1 tablespoon of red bean paste to the center of the dough, gather the outer edges of the dough and pinch to close. Place the buns, seam side down, onto a piece of parchment paper or plate 1 inch apart (they will expand)
Bringing water to a simmer in your steamer. Steam your buns for 10 minutes.