Preheat oven to 375°F (190°C). Grease a loaf pan and set aside.
Cook bacon in a skillet until crispy. Remove and crumble. In the same pan, sauté chopped onions and mushrooms until softened. Let cool slightly.
In a large bowl, mix ground beef, ground pork, breadcrumbs, milk, Parmesan cheese, sautéed vegetables, bacon, 1 cup Swiss cheese, eggs, Worcestershire sauce, 1 tbsp ketchup, garlic powder, thyme, salt, and pepper. Gently combine — don’t overmix.
Add half the meat mixture to the loaf pan. Create a shallow trench in the center and layer with a bit more Swiss cheese. Top with the remaining meat mixture, sealing the cheese in the center.
Spread ½ cup ketchup evenly over the top of the loaf.
Bake for 60–70 minutes, or until the internal temperature reaches 160°F (71°C).
Rest for 10 minutes before slicing to allow juices to redistribute. Serve warm.