Heat 1 tsp oil in skillet over medium; thinly slice onion + sauté 8-10 min until browned; season with salt + add 2 tbsp water; cover + cook 3-5 min until softened; set aside

Heat lightly oiled skillet over med-high, pat beef dry, add to pan in one layer + sear 2 min (for well done add 1 min); flip + cook 1 more min, season with salt/pep

Meanwhile in a small pot, heat ½ container of sauce with 2 slices cheese over med until melted + smooth, about 2-3 min

Toast 2 buns until warm + golden; top buns with beef + onions then close the lid; serve cheesy sauce on the side for dipping, looks good!