In a skillet, brown beef with onion until fully cooked and no longer pink. Drain off any grease.
Add the Manwich, cumin, black beans, and frozen corn to the beef. Bring mixture to a simmer and allow to simmer for 5 minutes.
Divide meat mixture between pita/flatbread breads. Serve topped with shredded lettuce, and cotija cheese along with cilantro and a squeeze of lime juice from the lime wedges.