Thinly sliced whole wheat bread (about 3 by 3-inches wide), as needed
To make the Arctic Char: Thinly slice the Arctic char into 1/4-inch thick slices and rub them with kosher salt. In a bowl, whisk together the vinegar, sugar, and ginger. Put the arctic char in the vinegar mix and refrigerate for 1 hour.
To make the Lemon-Marinated Cucumber Salad: Using a Japanese-style mandolin, julienne the cucumber and transfer to a bowl. Add the lemon juice and peel, sugar, and dill. Season with sea salt, to taste.
To make the Horseradish Cream: In a bowl, whisk together all of the ingredients and season with salt and pepper, to taste.
To serve, spread the bread slices with the cream and top with the Arctic char and cucumber salad.