These meatballs are tasty and well-seasoned as-is, but the recipe was designed to be a blank slate. Get creative, and you can change their flavor to fit the meal. Add 1 or 2 minced cloves of garlic and 1 teaspoon powdered dry ginger and they are Asian-inspired, prefect for a rice bowl or dipping in hoisin sauce. Add 1 or 2 minced cloves of garlic and some crushed red pepper and fennel seed, and they are Italian and can be added to a tomato sauce and served over pasta.
A food processor is ideal for finely chopping the mushrooms, but you can get the job done with a large chef's knife, too.