2) Prepare the curry butter: Combine ingredients in a food processor and pulse until smooth.
3) To prepare the salmon and mussels: Begin by making a seasoning with fennel and coriander seed and salt and pepper. Pound spices in a mortar and pestle, or grind with a coffee grinder, until you have a rough powder.
4) In a large mixing bowl combine couscous, corainder, lemon zest and half the spice mix. Stir well to combine, drizzle with olive oil, then divide evenly among 4 large pieces of parchment (big enough to create a folded pocket for the salmon). Nestle into the couscous 1 frozen chicken stock cube for each portion. Top with the piece of salmon and then sprinkle with remaining spice mix. Squeeze lemon juice over the top of each piece of fish and couscous then set 4 mussels around the fish in each packet. Fold over the parchment to create a pocket and trim paper to make a heart shape. Crimp over the edges, working from one end to the other to secure the paper tightly then brush with olive oil so the paper doesn't burn. Carefully transfer the parchment pockets to the hot sheet trays (you will probably need to put 2 per tray) then bake in the oven for 20 to 25 minutes.
5) When done, the paper will puff up. Cut open tableside with scissors, top with curry butter, and shower with fresh chopped spring onion and corainder.