In a large skillet, melt a tablespoon of butter over medium heat. Add thinly sliced onions and sauté them for about 10 to 15 minutes, until they are soft and golden brown.

Once the onions are caramelized, push them to the side and add one pound of ground beef. Cook it on medium-high heat for 5 to 7 minutes, breaking it up until fully browned.

Stir in a splash of gluten-free soy sauce, and add optional mushrooms or bell peppers if desired. Mix well and allow to cook for an additional 3 to 4 minutes.

Top the mixture with shredded cheese, lower the heat, and cover the skillet. Cook for 2 to 3 minutes, until the cheese is melted.

Spoon the mixture onto lightly toasted buns, ensuring a generous portion of the beef and onion blend.

Serve with a side of oven-baked fries, coleslaw, or a garden salad.