In a large skillet, combine 2 tablespoons of olive oil and heat over medium heat. Add 2 sliced yellow onions and cook, stirring occasionally, for about 15 minutes, or until golden brown.

Increase heat to medium-high and add 1 pound of ground beef. Break apart and season with 2 tablespoons of gluten-free soy sauce. Cook for about 5 minutes, until browned.

Lower heat to medium and sprinkle 1 cup of shredded Swiss cheese over the mixture. Cover and allow cheese to melt for 2-3 minutes.

Preheat oven to 350°F (175°C). Place buns on a baking sheet and toast for 5-7 minutes, until golden.

Spoon the beef and onion mixture onto the toasted buns generously. Serve hot.