Preheat oven to 375°F (190°C).
Clean mushroom caps and remove stems. (Chop stems finely if using in filling.)
Heat olive oil in a skillet over medium heat. Sauté minced garlic (and chopped mushroom stems if using) for 2-3 minutes.
In a bowl, combine sautéed garlic, gluten-free breadcrumbs, parsley, basil (if using), salt, pepper, goat cheese, and Parmesan cheese. Mix well. Add pine nuts or walnuts if desired.
Spoon filling into mushroom caps.
Arrange stuffed mushrooms on a parchment-lined baking sheet. Bake for 15-20 minutes until mushrooms are tender and tops are golden.
Serve warm as an appetizer or side dish.
