You need to start making the duck prosciutto about a month ahead. While the duck is still frozen, cut the fat from the skin side (it is then much easier to do-but so take care, the knife can easily slip on the frozen fat). Make sure to leave a thin layer of fat on the duck breast. On the flesh side, remove the connective tissue. Once the duck breast has thawed, place it in a roasting pan, skin side down.
Mix the salt, sugar, star anise, nutmeg, bay, coriander seed, pepper and lemongrass, then spread this over the duck, making sure it is completely covered. Cover with cling film, then a baking tray, and weigh down with cans or similar (the more weight the better)and leave to cure for 48 hours. When cured, remove the covering and wash off the mixture with water, then pat dry.
Smoke the duck lightly with lemongrass for 5 minutes. Once smoked, wrap the duck breast in cheesecloth and refrigerate for 21-30 days. At the end of this time, place in a freezer and when ready to serve, use an electric slicer to cut it into very thin slices. If you do not have an electric slicer, then it would be easier to omit the freezing and just cut the duck as thinly as possible using a very sharp knife.
In a mixing bowl, toss together all the salad ingredients. Once well incorporated, throw in about half the duck confit and half the prosciutto. Mix well and dress with nuoc cham sauce. Season with salt and pepper if necessary. Place the mixture in the middle of the plate. Mix the last of the duck confit and prosciutto, and mix well, then place on top of the mound as garnish. If you like, encircle the dish with a little ginger syrup and lemon oil.