Preheat oven to 400°. 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. , Flatten half the biscuits into 4-in. circles; arrange on greased 15x10x1-in. baking pans. 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. , Bake until golden brown, 12-15 minutes.