Begin by finely chopping your onions and any optional veggies like mushrooms or bell peppers if you're using them. Set aside the chopped ingredients in separate bowls.

In a large skillet, heat a drizzle of oil over medium heat. Add the chopped onions and sauté them for about 15 minutes, stirring occasionally, until they are golden brown and sweetly aromatic.

Once the onions are perfectly caramelized, push them to one side of the skillet and add the ground beef to the other side. Break the meat apart as it cooks, allowing it to brown evenly for about 5–7 minutes.

Next, stir in the gluten-free soy sauce along with any optional veggies like mushrooms or bell peppers you’d desire. Cook everything together for an additional 3–5 minutes.

Prepare your buns by lightly toasting them in a toaster or on a skillet. Pile generous scoops of the beef mixture onto the toasted buns.

Sprinkle a handful of shredded cheese over the beef mixture. Cover the skillet with a lid or briefly place the open sandwiches in a warm oven (about 350°F) for a few minutes to melt the cheese.