Finely chop ½ onion; heat 1 tbsp oil in a large skillet over med-high; add beef + onion to pan, break into large chunks + sear undisturbed 4-5 min; flip meat over, season generously with salt/pep + ½ of taco seasoning, then break into small pieces; cook 3-5 min until fully cooked + no pinkness remains

Fill 4 corn tortillas with ground beef; preheat air fryer to 400°; place filled tacos on sides in air fryer then spray or brush with 1 tbsp oil or cooking spray; air fry in batches 4-6 min until golden + crispy

Meanwhile, cut lettuce into shreds; stack 4 tortillas on a plate + wrap with a damp paper towel; microwave 15-30 sec or until warm + soft

Sprinkle hot flour tortillas each with 1 tbsp cheese then immediately wrap around stuffed corn tortillas; top each taco with 2 tbsp cheese, shredded lettuce + spicy ranch