Cook the Mushrooms:
Heat olive oil or butter in a large skillet over medium heat. Add the sliced mushrooms and cook, stirring occasionally, until they soften and release their moisture, about 7-10 minutes. Season with garlic powder, onion powder, salt, and pepper. Set aside.

Cook the Protein (if using):
If you’re using beef patties, chicken breasts, or turkey patties, cook them according to your preference. Season with salt and pepper. For burgers, cook on medium-high heat for about 4-5 minutes per side until the meat reaches the desired doneness. For chicken or turkey, cook until the internal temperature reaches 165°F (74°C).

Toast the Buns:
While the protein cooks, spread butter on the cut sides of your sandwich buns. Toast them on a skillet or in a toaster oven until golden and crispy.

Assemble the Sandwiches:
Place the cooked protein (beef patty, chicken, or turkey) on the bottom half of each toasted bun. Layer a generous amount of sautéed mushrooms on top of the protein, followed by two slices of Swiss cheese per sandwich.

Melt the Cheese:
Place the sandwiches under a broiler or in a microwave for 30 seconds, just until the Swiss cheese melts and becomes gooey.

Serve:
Top with fresh lettuce, tomato slices, or pickles, if desired. Garnish with fresh parsley for an added touch of color.