Preheat your oven to 375°F (190°C) and line a baking sheet with parchment paper.
Clean the mushrooms with a damp paper towel and remove the stems. Arrange them cavity-side up on the baking sheet.
In a small bowl, mix softened butter with minced garlic, parsley, lemon juice, salt, and pepper until well combined.
Fill each mushroom cap generously with the garlic butter mixture, pressing lightly to ensure even distribution.
If desired, sprinkle breadcrumbs on top for a crispy finish.
Bake for 12-15 minutes or until the mushrooms are tender and the butter is bubbling.
Serve immediately, garnished with fresh parsley and an extra squeeze of lemon, if desired.