Slice the onions thinly and heat a large skillet over medium heat. Add a drizzle of oil and toss in the onions, stirring frequently. Caramelize them for about 10-15 minutes until they turn golden brown and fragrant.

Once the onions are caramelized, add the ground beef to the skillet, breaking it apart with a spatula. Cook for about 5-7 minutes, stirring occasionally, until browned and fully cooked.

Pour in the gluten-free soy sauce and mix thoroughly. Let simmer for another 2 minutes to meld flavors.

Sprinkle shredded cheese generously over the mixture, cover the skillet with a lid and reduce heat to low. Allow the cheese to melt for about 2-3 minutes.

Prepare toasted buns and spoon generous servings of the beef and onion mixture onto each bun before serving hot.