Boil the diced potatoes in a large pot of salted water until tender, then drain and let them cool slightly.

In a mixing bowl, combine the cooled potatoes with thinly sliced red onion, chopped parsley, and chopped dill.

In a separate small bowl, whisk together olive oil, lemon juice, red wine vinegar, salt, black pepper, and red pepper flakes (if using) to create the dressing.

Pour the dressing over the potato mixture and gently toss everything together until well combined.

Taste and adjust seasonings as needed, then cover and refrigerate for at least 30 minutes before serving.