Preparation

• Heat the oven to 475°F.
• Toss the potatoes with 1 Tbs. of the oil and 1/4 tsp. salt on a large rimmed baking sheet. Arrange in a single layer, then roast until golden brown on the bottom, 13 to 15 minutes.
• Meanwhile, toss the green beans with a little olive oil and season with salt. Flip the potatoes (scrape up with a metal spatula, if needed), move them onto one half of the baking sheet, and spread the green beans on the other half in a single layer. Roast until the potatoes are tender and the green beans are browned in spots on the bottom, 12 to 15 minutes more.
• Meanwhile, in a small bowl, whisk the remaining 1-1/2 Tbs. oil, lemon zest and juice, garlic, and mustard. Stir in the dill, and season to taste with salt and pepper. Toss the green beans and potatoes with the dressing, and serve warm or at room temperature.