Cut the cucumber in half. Peel one half of the cucumber. Slice the remaining half (with peel) of the cucumber in thin slices and set aside.
Using a box grater, coarsely grate the peeled cucumber lengthwise, stopping when you get to the seedy center. Scrape the grated cucumber in a small mixing bowl and stir in the vinegar, lemon juice, sugar, salt and red onion. Set aside for at least 15 minutes.
Brush the sliced bread on one side with the olive oil and place on a baking sheet. Broil in the oven until lightly browned. Remove from the oven and set aside to cool.
Strain the cucumbers through a fine mesh sieve and press gently to remove all the excess liquid. Return the drained cucumber to the small mixing bowl and blend with the softened cream cheese and minced scallion.
To serve divide the cream cheese mixture on the bread. Top with cucumber slices, smoke salmon, capers and a sprinkle of flour de sel and fresh ground black pepper.