1. Remove the skin from the turkey breast and place the meat between two sheets of cling film on a hard surface. Flatten the meat to a thickness of about 1,5cm using a meat mallet or rolling pin.
2. Heat the butter in a saucepan. Add the onion and sauté over a medium heat until soft. Add the garlic and sauté for a further minute. Add the sweet potato, ginger and chillies. Stir well, then cover and allow to cook gently until just tender. Stir a few times to prevent sticking.
3. Remove from the heat and set aside to cool. Stir in the lemon zest, parsley, nuts and breadcrumbs. Stir in the egg yolks and season well with salt and freshly ground black pepper.
4. Spread the mixture out over the meat, then roll up like a Swiss roll. Place in a greased roasting tin and cover with strips of bacon, securing the bacon with toothpicks. Secure the roll with lengths of string, then roast in a preheated oven for one hour or until cooked through.
5. Remove the meat from the oven after roasting. Remove the toothpicks and string, and allow to rest for 10 minutes before cutting into slices. Serve with cranberry or apple jelly.