Peel the cucumber and cut it in half lengthwise. Scrape out the seeds with a small spoon. Chop half of the cucumber roughly and toss it into a blender. Cut the other half into neat slices and set them aside.

Add the oil, dill, parsley, lemon juice, shallot, and vinegar to the blender. Blend at low speed until smooth. Add salt and pepper to taste. Pour all but about 3 tablespoons of the dressing into a large mixing bowl.

Add the mesclun and sliced cukes to the bowl and toss until the greens are coated. Divide the salmon between two plates, arranging it in the middle of the plate. Surround with salad and then drizzle everything with the remaining dressing, some fresh dill, and a few grinds of cracked pepper.