Preheat the oven to 450°F.
In an enormous bowl, toss the potatoes with 2 tablespoons of the olive oil, ½ teaspoon sea salt and ½ teaspoon pepper. Distribute them out on a 9-by-13-inch sheet pan, reserving the bowl, and roast within the oven for quarter-hour.
Within the meantime, in the same bowl, toss the string beans with 1 tablespoon of the olive oil, ½ teaspoon sea salt and ½ teaspoon pepper and set aside.
Make the Dijon-walnut mixture. In a small bowl, mix collectively the walnuts, Dijon, remaining 1 tablespoon olive oil, lemon juice, parsley and ¼ teaspoon sea salt. Unfold the combination above the flesh side of the salmon fillets.
When the potatoes have cooked for quarter-hour, embrace the salmon to the sheet pan, pushing the potatoes aside, as wished. Add the string beans, becoming them in throughout the pan. Roast for about quarter-hour extra or till lastly virtually the whole lot is cooked to your liking.
