01 - Bring a large pot of salted water to a rolling boil. Add the trimmed green beans and cook for 2-3 minutes until just tender-crisp. Drain immediately.
02 - Transfer the blanched beans to a bowl of ice water to halt cooking and preserve bright color. Let cool completely, then drain thoroughly.
03 - In a large mixing bowl, combine the cooled green beans, sliced red onion, halved cherry tomatoes, and chopped parsley.
04 - In a small bowl, whisk together olive oil, lemon juice, Dijon mustard, minced garlic, salt, and pepper until thoroughly emulsified.
05 - Pour the vinaigrette over the vegetable mixture. Toss gently but thoroughly to coat all ingredients evenly.
06 - Sprinkle crumbled feta cheese over the salad just before serving. Serve chilled or at room temperature.