Preheat your oven to 350°F (175°C). Prepare your ingredients while the oven warms up.

In a large skillet, heat a drizzle of olive oil over medium heat. Add the ground beef and cook for 5-7 minutes until browned and no longer pink. Season with salt and pepper, then remove from skillet.

Using the same skillet, add more olive oil if necessary. Sauté the chopped onions and sliced mushrooms for 5-7 minutes until tender. Stir in minced garlic and cook for an additional minute.

Return the cooked ground beef to the skillet, and add Worcestershire sauce, soy sauce, Dijon mustard, and beef broth. Let simmer for about 5 minutes.

Stir in the sour cream until fully incorporated. Turn off the heat.

Cube the hamburger buns and layer them in a greased casserole dish. Spread the beef and mushroom mixture over the buns.

Sprinkle shredded Swiss cheese over the top. Bake for 25-30 minutes until the cheese is bubbling and golden brown.

Remove from oven and garnish with freshly chopped parsley. Allow to cool slightly before serving.