1 cup sliced mushrooms
1 onion, thinly sliced
Oil, for cooking
1 pound ground beef, shaped into 4 patties
4 burger buns
4 slices Swiss cheese
In a large pan, add a splash of oil, plus the mushrooms and onions, and heat on low 10-15 minutes.
While vegetables cook, add another splash of oil to a separate large pan. Season patties generously with salt and pepper, and cook on medium heat, 3-5 minutes per side or until cooked as desired. With about one minute left, add cheese to patties and cover with a lid to melt.
Top burger buns with patties, mushrooms, and onions, and serve.