Add chicken, remaining pesto, egg, breadcrumbs or almond meal, and parmesan cheese to a medium bowl. Mix well. Form into 12 (approximately 1-2 inch) meatballs. Arrange meatballs in prepared baking dish. Top with remaining marinara mixture. Arrange mozzarella slices on top of meatballs (like a blanket). Bake at 350 for 30 minutes.