Spray a 9×13 baking dish.
Cook beef with onion and seasonings.
Mix mayonnaise, sriracha, lime, garlic, salt.
Stir mayo and cheddar into beef.
Layer bottom buns, cheese, beef.
Add aioli and remaining cheese.
Place top buns, brush butter, add sesame.
Bake at 375°F for 15–20 minutes.
Rest briefly, slice, serve.