Bring a large pot of water to a boil, then add the cubed Yukon gold potatoes and cook until tender, 10-12 minutes. Look for the cubes to be easily pierced with a fork.

Drain the potatoes in a colander and let them cool until just warm or room temperature, 10-15 minutes. They should look matte rather than steaming hot.

In a bowl, whisk together mayonnaise, lemon juice, lemon zest, olive oil, and Dijon mustard until smooth and glossy, 30-60 seconds. The dressing should look uniformly pale and thick.

In a mixing bowl, combine the cooled potatoes with chopped parsley and sliced green onions. Toss until the herbs and onions are evenly distributed.

Pour the dressing over the potatoes and toss until every cube is coated. The potatoes should glisten with a light, creamy coating.

Season with salt and pepper to taste and toss once more to distribute. Stop when the flavor pops but the salad still feels light.

Refrigerate the lemon potato salad for 2 hours before serving. The salad should look set and well-mixed, not watery.