Chinese Steamed Buns with Barbecued Pork Filling

Name: Chinese Steamed Buns with Barbecued Pork Filling
Ingredients: 1 (.25 ounce) envelope active dry yeast; 1 cup lukewarm water; 4.5 cups all-purpose flour; 0.25 cup white sugar; 2 tablespoons shortening or vegetable oil; 0.5 cup boiling water; 2 tablespoons sesame oil; 2 tablespoons vegetable oil; 1 green onion, thinly sliced; 1 clove garlic, minced; 0.5 pound Asian barbequed pork, cubed; 2 tablespoons light soy sauce; 2 tablespoons oyster sauce; 1 tablespoon white sugar; 1 tablespoon cornstarch; 2 tablespoons water