Proof the yeast by adding the sugar and about three tablespoons of warm water. Let the mixture sit for about five minutes. Make sure bubbles form in the mixture. Add the flour, salt, vegetable oil and the rest of the water to the proven yeast. Knead the dough until smooth. Put the dough in a bowl that will contain double of its size. Cover with plastic wrap or a wet towel. Let the dough rise in a warm spot.

Wash and blanch the radish greens in hot water for about one minute or until just wilted. Drain and squeeze all excess water from the greens. Cut the radish greens into small pieces of about 1/8-inch wide. In a medium mixing bowl combine all the filling ingredients and set aside.

After about one hour, or when the dough has doubled in size punch it down and sprinkle it with the baking soda. Knead the dough for about three minutes or until the baking soda is evenly distributed.

Divide the dough into four equal portions. Roll one of the portions into a cylinder about six inches long. Cut the dough into six equal portions. Roll each piece into a ball with your hands. Flatten and roll each call into a five-inch diameter round using a rolling pin.

Put a dough round on one of your palms. Scoop about two tablespoonsful of the filling onto the center of the dough. With the other hand starting on one edge of the dough, use your thumb and index finger to pleat the dough as you turn the bun around in your palm.

Arrange the sealed buns in two twelve-inch diameter bamboo steamers lined with perforated wax paper or cheesecloth. Be sure the allow enough room between the buns for them to expand. Put the steamers over boiling water in a wok and steam for about ten minutes. Serve these buns piping hot.