Preheat the oven to 375 degrees and line a baking sheet with parchment paper.
Heat a skillet over medium heat and cook the chopped mushrooms and diced onion until the liquid evaporates and the vegetables soften, about 6 minutes. Add the minced garlic and cook 1 minute more, then remove from heat and let cool slightly.
In a large bowl, combine the ground turkey, cooled mushroom mixture, 3/4 cup of the shredded Swiss cheese, breadcrumbs, egg, thyme, Worcestershire sauce, salt, and black pepper. Mix gently until just combined.
Shape the mixture into a loaf on the prepared baking sheet. Sprinkle the remaining 1/4 cup Swiss cheese over the top.
Bake for 45 to 50 minutes until the internal temperature reaches 165 degrees. Let the meatloaf rest 10 minutes before slicing.