Preheat the oven to 375 degrees and line a baking sheet with parchment paper.
In a mixing bowl, combine the cream cheese, mozzarella cheese, minced garlic, salt, pepper, and parsley until smooth.
Spoon the cheese mixture into each mushroom cap, filling them evenly and mounding the top slightly.
Place the filled mushrooms on the baking sheet and bake for 18 to 20 minutes until the mushrooms soften and the cheese melts.
Remove from the oven and let them cool for 2 minutes. Press two olive slices onto each mushroom to form ghost eyes.