Heat a tablespoon of oil in a large skillet over high heat. Add the sliced onions and mushrooms, sautéing until they achieve a golden brown color. Season with salt and set the mixture aside.

In a bowl, combine the ground beef with the seasoning, mixing it well with your hands. Shape the mixture into burger patties that are about 3/4-inch thick, slightly larger than the buns.

Using the same skillet, cook the patties over medium heat, pressing down gently as they cook. Each side should take around five minutes, or until the internal temperature hits 165°F. Add the cheese on top just before removing the patties from the heat.

To assemble, place a patty on the bottom half of a bun, followed by a generous portion of the onion and mushroom mixture. Add the top bun, which you can spread with ketchup, mayonnaise, or your favorite condiment. Repeat for the remaining burgers.

Allow the burgers to rest for a couple of minutes, then dig in and enjoy!