Wash potatoes and transfer to a large pot. Fill pot with cold water, covering the potatoes by 1 inch.
Bring the potatoes to a boil over high heat and then lower to a simmer. Cook until potatoes are fork tender but with a slight firmness, about 20-25 minutes.
Drain and let potatoes cool to room temperature.
In a large bowl, whisk together red wine vinegar, lemon juice, honey, salt, olive oil, and Dijon mustard.
Once cooled, cut the potatoes into fourths and transfer to a serving dish. Add green onion, chopped celery, sliced radishes, pepper, Kalamata olives and toss with vinaigrette and chopped Italian parsley. Garnish with fresh parsley leaves.
Notes
Additional flavor if desired: 1/4 tsp thyme, oregano, or basil.