Boil potatoes:

Cut the potatoes in half. Place them in a large pot and cover with water. Bring to a boil and cook until just fork-tender.

Add string beans:

During the last 5 minutes of boiling, add the string beans to the pot. Cook until tender yet crisp. Drain both potatoes and beans.

Whisk dressing:

In a small bowl, whisk together the lemon zest, lemon juice, olive oil, apple cider vinegar, cracked pepper, and salt.

Slice onion and scallions:

Thinly slice the red onion and chop the scallions.

Toss salad with dressing:

In a large mixing bowl, combine the cooked potatoes, string beans, red onion, and scallions. Pour the dressing over the mixture and toss gently to coat. Adjust seasoning with additional salt if needed.