Place the pork slices in a large bowl. Add Gochujang sauce and soy sauce, toss to coat. Cover with plastic wrap and marinate for 2-24 hours in the refrigerator.
Preheat the air fryer to 400°F. Working in batches, arrange a single layer of pork in the air fryer, discarding excess marinade. Cook for about 10 minutes, flipping halfway until browned and reaches an internal temperature of 145° F. To serve, divide brown rice among the 12 lettuce leaves. Top with pork, cucumber, carrots, sesame seeds, scallions, and Gochujang sauce.