Preheat your oven to 350°F (175°C).

In a large skillet, heat about a tablespoon of olive oil over medium heat. Add the ground beef and season with salt and pepper. Cook for approximately 5–7 minutes until browned. Remove from skillet and set aside.

Using the same skillet, add a bit more olive oil if necessary, then add diced onions and sliced mushrooms. Sauté for 5–7 minutes until softened. Add minced garlic and cook for another minute.

Return the browned ground beef to the skillet together with the mushroom and onion mixture. Pour in Worcestershire sauce, soy sauce, Dijon mustard, and beef broth. Let simmer for 5 minutes and mix in sour cream.

Cut the hamburger buns into cubes and layer them evenly on the bottom of a casserole dish. Pour the beef mixture over the buns.

Sprinkle Swiss cheese generously over the top. Bake in the preheated oven for 25–30 minutes or until the cheese is melted and bubbly.

Remove from the oven and let cool slightly. Garnish with freshly chopped parsley before serving.