Preheat the oven to 400°F and line a large baking sheet with parchment paper.

Heat a skillet over medium heat and cook the mushrooms and onion until softened and any liquid evaporates, about 5 minutes. Let cool slightly.

In a large bowl, combine the ground beef, cooked mushroom mixture, egg, breadcrumbs, half the Swiss cheese, and a pinch of salt and pepper. Mix gently until just combined.

Divide the mixture into four portions and shape each into a small loaf. Wrap two slices of bacon around each loaf, tucking the ends underneath.

Place the loaves on one side of the baking sheet. On the other side, toss the halved potatoes with olive oil, minced garlic, salt, and pepper, then spread them in a single layer.

Bake for 25 to 30 minutes until the meatloaves reach 160°F internally and the bacon is crisp. Sprinkle the remaining Swiss cheese over the loaves for the last 5 minutes of baking.

Remove from the oven, let rest for 5 minutes, then sprinkle with chopped parsley before serving.