Preheat your oven to 375°F (190°C).
Clean the mushrooms and remove stems. Set aside caps, and finely chop stems.
In a skillet, heat some olive oil over medium heat and sauté the minced garlic until fragrant.
Add chopped spinach, artichokes, and chopped mushroom stems to the skillet. Cook until spinach wilts.
In a bowl, combine the sautéed mixture with cream cheese, Parmesan, mozzarella, red pepper flakes, salt, and pepper.
Fill each mushroom cap generously with the cheese and spinach mixture.
Place the stuffed mushrooms on a baking sheet and drizzle with olive oil.
Bake in the preheated oven for 20-25 minutes until the mushrooms are tender and tops are golden.
Remove from oven and let cool for a few minutes before serving.