In a large skillet, cook beef and onion over medium heat until meat is no longer pink, 5-7 minutes, breaking into crumbles; drain. Add taco seasoning and prepare according to package directions. Cool slightly. , Preheat air fryer to 350°. Flatten half the biscuits into 4-in. circles. Spoon 1/4 cup meat mixture onto each circle; sprinkle each with 1/4 cup cheese. Flatten remaining biscuits; place over filling and pinch edges to seal tightly. , In batches, place puffs in a single layer in greased air fryer. Cook until golden brown and puffed, 10-15 minutes.