This recipe is best served at room temperature, and since it does not contain mayo, there is no need to worry about spoiling.
1 pound baby potatoes, halved
1 ½ cups of fresh green beans, trimmed and halved
1 pint (2 cups) cherry tomatoes, halved
2 celery stalks, thinly sliced
3 scallions, thinly sliced
1/3 cup kalamata olives, halved
1/3 cup chopped fresh flat-leaf parsley
2 tablespoons capers
2 tablespoons dijon mustard
1 ½ tablespoons whole-grain mustard
1 large lemon, zested and juiced
1/4-cup extra-virgin olive oil
Kosher salt and freshly ground black pepper
Prepare an ice bath (large bowl of ice water) and medium pot of boiling water. Add green beans to the pot of boiling water and blanch for one minute. Use a large slotted spoon to transfer the green beans from the pot to the ice bath to stop the cooking and preserve color. Strain green beans in a colander and set aside.
Add the potatoes to the boiling pot of water. Boil potatoes until they are fork-tender, about 15 to 20 minutes. Drain the potatoes in a colander and allow them to dry for 10 minutes.
While potatoes cool, prepare the dressing by adding Dijon mustard, whole-grain mustard, lemon zest and lemon juice to a bowl. Whisk in olive oil and season with salt and pepper to taste.
In a large serving bowl, add the potatoes, green beans, tomatoes, celery, scallions, olives, parsley, capers, and mustard dressing. Toss gently until all the ingredients are coated in dressing and season with salt and pepper, to taste. Serve at room temperature or chilled.