Preheat oven to 375°F (190°C) and prepare baking sheet with parchment.
Clean mushrooms, remove stems, chop stems finely.
Brush mushroom caps with olive oil, arrange cavity-side up.
Mix cream cheese, pesto, garlic, stems, parmesan, pine nuts, basil, salt & pepper until smooth.
Stuff mushroom caps with filling, top with parmesan, mozzarella, and breadcrumbs if using.
Bake 18–22 minutes until mushrooms are tender and cheese is golden.
Cool 3–5 minutes, garnish with basil, serve warm.