Preheat oven to 375°F (190°C). In large bowl, stir together bread crumbs, onion, egg, parsley, chives, mustard, garlic, Worcestershire sauce, salt and pepper until well combined. Crumble in ground chicken; mix gently to combine.
Roll into 18 meatballs; arrange on greased foil-lined baking sheet. Lightly coat meatballs with nonstick cooking spray. Bake for 15 to 20 minutes or until golden brown and cooked through.
Mac & Cheese
Meanwhile, melt butter in large saucepan set over medium heat; sprinkle flour over top. Cook, stirring constantly, for about 2 minutes or until lightly browned. Slowly whisk in some of the milk until smooth. Add remaining milk, along with mustard, garlic, salt and pepper. Bring to simmer; cook for about 5 minutes or until thickened.
Remove from heat. Whisk in Cheddar, Gruyère and Parmesan, a handful at a time, until melted and well combined. Stir in pasta. Serve immediately with meatballs.
Tip: Use damp hands to avoid the raw chicken mixture from sticking when rolling into meatballs.