To prepare the filling, rub five-spice powder evenly over pork. Heat a grill pan over medium-high heat. Coat the pan with cooking spray. Add pork to pan; cook 18 minutes or until a thermometer registers 155°, turning pork occasionally. Remove pork from pan, and let stand 15 minutes.
Cut pork crosswise into thin slices; cut slices into thin strips. Place pork in a medium bowl. Add onions, hoisin sauce, vinegar, soy sauce, honey, ginger, garlic and 1/4 teaspoon salt; stir well to combine. Cover and refrigerate.
To prepare dough, combine 1 cup warm water, sugar and yeast in a large bowl; let stand 5 minutes.
Lightly spoon flour into dry measuring cups; level with a knife. Add flour, oil and 1/4 teaspoon salt to yeast mixture; stir until a soft dough forms. Turn dough out onto a lightly floured surface. Knead until smooth and elastic (about 10 minutes). Place dough in a large bowl coated with cooking spray, turning to coat top. Cover and let rise in a warm place (85°F), free from drafts, 1 hour or until doubled in size. (Gently press two fingers into dough. If indentation remains, dough has risen enough.)
Punch dough down; let rest 5 minutes. Turn dough out onto a clean surface; knead in baking powder. Let dough rest 5 minutes.
Divide dough into 10 equal portions, forming each into a ball. Working with one dough ball at a time (cover remaining dough balls to keep from drying), roll ball into a 5-inch circle. Place 1/4 cup filling in center of dough circle. Bring up sides to cover filling and meet on top. Pinch and seal closed with a twist. Repeat procedure with remaining dough balls and filling.
Arrange 5 buns seam side down, 1 inch apart, in each tier of a 2-tiered bamboo steamer. Stack tiers; cover with lid.
Add water to a large skillet to a depth of 1 inch; bring to a boil over medium-high heat. Place steamer in pan; steam 15 minutes or until puffed and set. Cool 10 minutes before serving.
Tip
Kick up the spice level with some red chili peppers, cilantro, or jalapeños. Tiny cubed cucumbers make a fresh, crunchy addition. Hint: The beauty of this recipe is that you don't have to stick with pork. Make it a veggie, bean or even seafood bun.
