Preheat oven to 400 F degrees. Line a rimmed baking sheet with parchment paper or foil and set aside.
To a small mixing bowl, combine cream cheese, bacon, cheese, jalapenos, garlic and salt and pepper. Stir well.
Spoon approximately 1 Tbsp of filling into each mushroom cap (this amount will vary depending on the size of your mushrooms), then sprinkle with additional cheese (if using).
Bake 20-25 minutes, until mushrooms are piping hot and cheese is lightly golden brown.
Carefully remove mushrooms from baking sheet (they won't feel very firm - a wide spatula is good for this), and let sit at room temperature on a plate for 5 minutes or so. Serve sprinkled with sliced green onions and/or minced parsley (if using).
