Preheat oven to 200C. Line a large baking tray with baking paper.
In a medium pan, fry the onion over gentle heat in a little olive oil until softened. Remove from heat and set aside.
In a large bowl, mix breadcrumbs, cranberries, pine nuts, dill, zest then add the softened onion. Mix to combine. Sprinkle 1or 2 tbs of water on the mixture if it seems too dry.
Place the salmon on the baking tray, and use paper towel to pat dry the inside of the salmon. Season the cavity with a little salt then fill with the stuffing. Lay the lemon slices over the top on the stuffing so they just peak out from the skin. These will turn golden and caramelised as the fish cooks. Use a sharp knife to make three slashes into the side of the salmon, about 1 cm deep and season the entire fish with salt.
Bake in the oven for 30 minutes or until done to your liking, 30 minutes and the fish will be a little pink inside, 45 minutes and it will be cooked all the way through.
Carefully transfer fish onto a large serving platter. Serve with all your favourite Christmas trimmings.
Note: The stuffing can be made a day ahead and stored in the fridge until needed. You can also cook the salmon on the BBQ. Line a large sheet of foil with baking paper, place the salmon on top, fill as above, then fold over salmon to seal.