Preheat the slow cooker if necessary; see the manufacturer's instructions. Put the chicken, onion and herbs into the slow cooker pot. Mix the stock, lemon rind and juice and salt and pepper then pour over the chicken.
Cover with the lid and cook on high for 30 minutes. Reduce the heat and cook on low for 5½–7½ hours, or set to auto for 6–8 hours, until the chicken is cooked through and tender. When almost ready to serve, bring a large saucepan of water to the boil, add the pasta and cook for 9–10 minutes or until just tender.
Meanwhile, drain the stock from the slow cooker pot into a second large saucepan and boil for 5 minutes until reduced by one-third or to about 200 ml (7 fl oz). Whisk the eggs and egg yolks in a bowl, then gradually whisk in 2 ladlefuls of stock until smooth. Pour into the reduced stock, then whisk over a gentle heat until the sauce has thickened slightly. Stir in the parsley.
Pour the sauce over the chicken. Spoon the pasta into shallow bowls and top with the chicken. Sprinkle with lemon rind curls and extra chopped parsley, if liked.