In a large pot, bring salted water to a boil. Add the baby potatoes and cook for about 10-12 minutes, or until tender. Add the green beans to the pot for the last 3-4 minutes of cooking. Drain and rinse under cold water to stop the cooking process.
In a large bowl, combine the olive oil, apple cider vinegar, Dijon mustard, salt, and pepper. Whisk until well combined.
Add the cooked potatoes and green beans to the bowl, along with the cherry tomatoes, red onion, and parsley. Gently toss to coat all the ingredients in the dressing.
Taste and adjust seasoning if necessary. Serve immediately or refrigerate for 30 minutes to allow flavors to meld.