Soak the cedar plank in water for at least 1 hour.
Finely grate enough zest from the oranges and the limes to make 1½ teaspoons of each; set aside. Squeeze 240 millilitres of juice from the oranges and 80 millilitres of juice from the limes. In a small saucepan over medium–high heat on the stove, combine the orange juice, lime juice, lemon juice and honey and bring to a boil. Continue to boil until the liquid is reduced to 180 millilitres, 10 to 14 minutes. Remove from the heat. Stir in the butter, the orange zest, lime zest and coriander. Let the glaze cool completely. Stir in the chopped fresh cilantro.
Place the salmon fillet on a large baking tray. Cut the fillet into six individual portions, cutting right down to the skin but not through it.
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In a small bowl combine the ground coriander, salt, cumin and pepper. Pour 120 millilitres of the citrus glaze slowly and evenly over the top of the salmon, reserving the remaining glaze for serving. Spread the glaze evenly over the salmon, brushing some glaze between the individual portions. Season the salmon evenly with the coriander–cumin mixture. Allow the salmon to marinate at a cool room temperature for 45 minutes, basting occasionally with any glaze that runs onto the baking sheet.
Meanwhile, make the salad: In a small bowl whisk the oil, orange juice, vinegar, ground coriander, salt and pepper until well blended and emulsified. Stir in the chopped cilantro and reserve the dressing at room temperature. In a large bowl combine the frisée, onion, dates and tangerines. Then cover and refrigerate until ready to serve.
Prepare the grill for indirect cooking over medium heat (180°C to 230°C).
Brush the cooking grates clean. Remove the soaked plank from the water and place it on the cooking grate over direct heat. Close the lid. After 5 to 10 minutes, when the plank begins to smoke and char, turn the plank over and place it over indirect medium heat. Put the salmon on the plank, skin-side down, and cook, with the lid closed, until the salmon is just opaque in the centre and begins to brown slightly around the edges, 25 to 35 minutes. Transfer the plank with the salmon to a heatproof surface. Slide a spatula between the skin and flesh and transfer to serving plates. Spoon some of the remaining citrus glaze over each serving. Gently toss the salad with the dressing and serve it alongside the salmon.