Preheat oven to 180°C. Line baking sheet with baking paper. In a large pan, heat butter over medium heat; cook onion and garlic until softened, approximately 5 to 7 minutes. Add spinach, salt and pepper; cook until wilted, approximately 5 minutes. Transfer to large bowl; let cool completely.

Stir in parsley, lemon juice and Worcestershire sauce. Stir in Mozzarella, Parmesan and eggs. Add breadcrumbs; mix well until mixture holds together (mixture will be a little wet.) Shape into 2-3 cm balls. Place on pre prepared baking sheet.

Bake until firm to the touch and golden brown, approximately 30 minutes. Let cool for 5 minutes before serving.