Place the quartered potatoes in a large pot and cover with cold, salted water. Bring to a boil and cook until fork-tender, about 15-20 minutes. Drain immediately.

While the potatoes cook, blanch the trimmed green beans in boiling salted water for 3-4 minutes until crisp-tender. Immediately transfer them to an ice bath to stop the cooking process. Drain well.

Prepare the vinaigrette by whisking together the olive oil, red wine vinegar, Dijon mustard, minced garlic, salt, and pepper until emulsified.

In a large bowl, combine the warm, drained potatoes and the crisp green beans. Drizzle about half of the vinaigrette over the warm mixture and gently toss to coat. The warm potatoes will absorb the dressing better.

Add the diced red onion, chopped hard-boiled eggs, and fresh parsley to the salad. Pour the remaining vinaigrette over the mixture and toss gently until everything is evenly coated. Taste and adjust seasoning if necessary.

Allow the salad to sit at room temperature for at least 15 minutes before serving to let the flavors meld. This salad can also be served chilled.