Caramelize the onions — Air fry sliced onions at 350°F for 8–10 minutes, tossing halfway, until golden and soft.
Season the beef — Combine ground beef with Worcestershire, garlic powder, onion powder, salt, and pepper. Form into 2 thin patties slightly larger than your bread.
Cook the patties — Air fry at 370°F for 6–8 minutes, flipping halfway, until cooked through (160°F internal).
Build the sandwich — Butter one side of each bread slice. On the unbuttered side, layer cheese, patty, caramelized onions, more cheese, then top slice (buttered side out).
Toast to golden — Air fry at 360°F for 3–4 minutes per side, until bread is crispy and cheese is fully melted. Slice and serve hot.