If preparing the buns, to a large bowl add the flour, yeast, baking powder and sugar; whisk to combine. Drizzle in ½ cup/120 milliliters room-temperature water while mixing the flour with one hand until the texture is fluffy and sandy. Transfer to a flat surface and knead the mixture with both hands, pushing it away from you with the heel of each hand until it comes together into a smooth ball of dough, 3 to 5 minutes. (It will transform from raggedy to tacky to supple.) Cover the dough with plastic wrap and let rest at room temperature for 20 minutes.

While the dough rests, prepare the lamb: Carefully slice the lamb as thinly as possible, ideally about ⅛-inch thick. Add the lamb to a medium bowl, and sprinkle with cornstarch and 4 teaspoons of the oil. Mix with your hands until the cornstarch has been evenly dispersed and dissolved; set aside.

After the dough has rested for 20 minutes, remove the plastic wrap and knead the dough a few more times. Cover with plastic wrap and let rest for another 10 minutes.

While the dough rests a second time, cook your filling: In a large skillet or wok, heat the remaining 3 tablespoons oil over high until shimmering. Add the scallions, ginger and garlic and sauté for 30 seconds. Add the lamb and stir-fry for about 5 minutes, until thoroughly browned in spots and cooked through. Turn the heat down to low and sprinkle with cumin, salt and chile powder; stir to combine. Stir in the onion and longhorn pepper; cover and set aside.

To shape the dough, take one piece and roll it between your palms into a ball. Place it on an unfloured work surface and press into a smooth, round mound. Use a small rolling pin to flatten to about 4-inches wide. Repeat with the remaining dough.

Set a small skillet over medium and warm it up for 5 minutes. Turn the heat down to low, and add one dough round. Cover the skillet and cook for 1 minute on each side, until some brown spots appear. Flip and cook again for 1 to 2 minutes on each side until fully cooked (no parts should look gray or raw). It should be crisp on the outside and steaming on the inside. Repeat with remaining 3 dough rounds, letting the skillet heat up for a couple minutes between batches.

Slice toasted bread in half and fill with warm lamb mixture. Enjoy immediately.