Preheat the oven to 350 degrees and lightly grease a loaf pan.
Heat a skillet over medium heat and cook the mushrooms and onion until the mushrooms release their liquid and the onion softens, about 5 minutes. Add the garlic and cook 1 minute more, then remove from heat and let cool slightly.
In a large bowl, combine the ground beef, cooled mushroom mixture, 1 cup of the Swiss cheese, breadcrumbs, eggs, Worcestershire sauce, salt, and pepper. Mix with your hands until just combined.
Press the mixture evenly into the prepared loaf pan. Sprinkle the remaining 1/2 cup Swiss cheese over the top.
Bake for 60 to 70 minutes until the internal temperature reaches 160 degrees. Let the meatloaf rest 10 minutes before slicing.