Step 1: In a bowl, combine flour, yeast, sugar, and salt. Add warm water and oil, mix until a dough forms.
Step 2: Knead dough on a floured surface for 5 minutes until smooth. Place in a greased bowl, cover, and let rise for 1 hour.
Step 3: While dough rises, cook ground beef in a pan over medium heat until browned. Drain excess fat.
Step 4: Add soy sauce, sesame oil, ginger, garlic, green onions, pepper, and cornstarch to beef. Stir well and cook for 2 minutes, then let cool.
Step 5: Punch down risen dough and divide into 8 equal pieces. Roll each piece into a ball, then flatten into a 4-inch circle.
Step 6: Place 1 tbsp of beef filling in center of each circle. Gather edges and pinch to seal, forming a bun.
Step 7: Place buns on parchment paper in a steamer basket, cover, and let rest for 15 minutes.
Step 8: Steam buns over boiling water for 15 minutes. Turn off heat and let sit for 5 minutes before serving.