1: Preheat the oven to 375°F.
2: In a pan, heat olive oil and sauté finely chopped onion until translucent.
3: Add chopped spinach and minced garlic, cooking until spinach wilts.
4: Mix in cream cheese, salt, and pepper until well combined.
5: Stuff each cleaned mushroom with the spinach filling.
6: Top stuffed mushrooms with mozzarella cheese.
7: Bake in the oven for 15-20 minutes or until mushrooms are tender and cheese is bubbly.
