In a skillet, heat olive oil over medium heat. Add sliced mushrooms and sauté for about 5 minutes until they begin to soften.

Stir in minced garlic and continue cooking for another 2-3 minutes until the garlic is fragrant and the mushrooms are golden brown. Season with salt and pepper to taste. Remove from heat and set aside.

In another skillet, melt butter over medium-low heat. Place two slices of sourdough bread in the skillet, and layer half of the cheddar and mozzarella cheese on top.

Spoon the sautéed mushroom and garlic mixture evenly over the cheese, then top with the remaining cheese. Place the second slice of bread on top to form a sandwich.

Cook the sandwich for about 4-5 minutes or until the bottom is golden brown. Carefully flip the sandwich and cook for an additional 4-5 minutes on the other side until the cheese is melted and the bread is crispy.

Repeat the process with the remaining ingredients to make a second sandwich.

Once both sandwiches are cooked, slice them in half and garnish with fresh parsley if desired. Serve warm.