Peel alternating strips from the cucumber, leaving some peel to create stripes, and slice into thin rounds. In a large bowl, combine the vinegar, sugar and some salt and pepper. Whisk in the olive oil, then 2 tablespoons of the dill. Add the cucumbers and toss.
Combine the creme fraiche, horseradish, mustard, lemon juice and the remaining 2 tablespoons dill in a small bowl. Season with salt and pepper.
Using a slotted spoon, scoop the cucumbers from the vinaigrette and mound on a large platter. Dip the leaf ends of the watercress in the remaining vinaigrette and mound on the platter. Toss the tomatoes in the vinaigrette, remove with a slotted spoon and mound on the platter. Lay the salmon over the mounds. Spoon the creme fraiche dressing over the top.
Garnish the platter with lemon wedges and serve immediately.
Recipe courtesy of Bobby Flay