Preheat your oven to 375°F (190°C).
Clean the mushrooms with a damp cloth and gently remove the stems. Finely chop the stems and set aside.
In a skillet over medium heat, cook the Italian sausage until browned. Add the chopped mushroom stems and minced garlic, cooking for an additional 2-3 minutes until softened. Remove from heat.
In a mixing bowl, combine the cooked sausage mixture with the cream cheese, Parmesan cheese, breadcrumbs, and parsley. Add salt and pepper to taste. Mix until well combined.
Using a spoon, fill each mushroom cap generously with the sausage mixture.
Place the stuffed mushrooms on a baking sheet lined with parchment paper or lightly greased with cooking spray. If desired, drizzle with a little olive oil.
Bake in the preheated oven for about 20 minutes, or until the mushrooms are tender and the tops are golden brown.
Remove from the oven and allow to cool slightly before serving.