Prepare the potatoes: Add the potatoes to a large bowl. Drizzle with 1 tbsp olive oil and toss to evenly coat them in the oil. Spread on a parchment-lined baking sheet. Sprinkle with salt and black pepper. Roast until the potatoes are beginning to brown and tender when a knife is inserted, 25-30 minutes.
Prepare the green beans: While the potatoes are roasting, add the green beans to the previously used large bowl. Drizzle with the remaining 1 tbsp oil, sprinkle with salt and black pepper, and toss to combine. When the potatoes are done roasting, add the green beans to the sheet pan with the potatoes. Return to the oven and roast until the green beans are crisp-tender, 5-7 minutes. Remove and set aside, and cool to room temperature.
2 lb trimmed green beans, 2 tbsp olive oil
Make the dressing: In a bowl, combine the mayonnaise, lemon juice, Dijon mustard, whole-grain mustard, honey, salt, black pepper, dill, parsley, and mint. Whisk and set aside.
¾ cup mayonnaise, 1 tbsp lemon juice, 1 tbsp Dijon mustard, 1 tbsp whole-grain mustard, 1 tbsp honey, ½ tsp kosher salt, ½ tsp freshly ground black pepper, 2 tbsp chopped fresh dill, ¼ cup chopped fresh parsley, 1 tbsp chopped fresh mint
Assemble: In a large bowl, combine the cooled potatoes, green beans, scallions, bacon, and dressing. Toss to combine and pour into a serving dish. Cover and refrigerate. Once chilled, serve.