Add the kale, breadcrumbs, minced garlic and half the onions to a large food processor and pulse together until very finely chopped. Add the egg, Parmesan and nutmeg and pulse together until combined.
CHILDREN: Tip into a large bowl, then add the turkey mince and mix together until well combined, trying not to overwork the meat. Shape into 18 meatballs and place on a baking sheet lined with baking paper. Cover and refrigerate for 30 minutes.
Add ½ tbsp oil to a large saucepan over a medium heat. Add the remaining onion along with the thyme and bay leaves and sauté for 6-8 minutes until softened. Add the thinly sliced garlic and cook for a further minute, then add the chopped tomatoes and passata. Fill the empty chopped tomato can halfway with water and add that to the pan too. Stir to combine, bring to a boil, then reduce the heat and leave to simmer for 10 minutes.
Meanwhile, heat the remaining oil in a large frying pan. Once the oil is hot, brown the meatballs in two batches, turning them over so they cook evenly. Transfer to a paper towel-lined plate while you cook the rest.
Once all the meatballs are browned, carefully add them to the simmering tomato sauce, cover and cook for 15 minutes. Once done, remove the thyme sprigs and bay leaves and sprinkle over the lemon zest.