What does blanching green beans mean? Cook fresh trimmed green beans in boiling, salted water 5-6 minutes; drain. Use immediately, or plunge into ice water to stop the cooking process; drain and pat dry.
Heat oven to 425 degrees F. On a large rimmed parchment-lined baking sheet, toss the potatoes, 1 Tbsp. oil, and 1/2 tsp. each salt and pepper. Roast for 15 minutes.
In a small bowl, whisk together the lemon juice, mustard, and remaining tablespoon oil. Stir in the parsley and lemon zest.
Add the (blanched) green beans to the pan with the potatoes; toss to combine. Push the potatoes and green beans to the edges of the pan.
Place the salmon in the center of the pan. Spread the herb mixture over the salmon, and roast until the salmon is opaque throughout, and the potatoes are golden brown and tender, 10 to 12 minutes.