For the salad: Quarter the cucumber, lengthwise, and remove the seeds, but leave on the skin. Thinly slice the cucumbers and mix with the salt in a colander. Set in the sink for about 1 hour to drain. Meanwhile, place the yogurt in a coffee filter-lined strainer and set over a bowl to drain, about 1 hour.
Rinse the cucumbers with cold, running water. Press down on the cucumbers to extract as much liquid as possible and pat dry. Toss the cucumbers with the drained yogurt, dill, sugar, orange zest, cayenne, and season with pepper, to taste.
Preheat the oven to 275 degrees F.
Cut the salmon lengthwise and then crosswise to make 4 equal squares of fish. Lightly sprinkle the salmon all over with a pinch of turmeric and rub in slightly to coat evenly. Season salmon with salt and pepper and place on a very lightly oiled oven-proof nonstick pan. Roast the salmon, turning the pieces carefully with a spatula after about 10 minutes, until just cooked through, about 20 minutes in all. (Slow-roasted salmon looks bright orange when done, and will be luscious in the center.) To serve, divide the cucumbers between 4 plates, top with the salmon and garnish with dill fronds.
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