Bring a large pot of salted water to a boil. Add the gold potatoes and cook until fork tender.
Drain the potatoes and place them into cold water to cool slightly. Once cool enough to handle, peel the skins off and chop the potatoes into medium bite-sized pieces.
In a bowl, combine the sliced red onion, red wine vinegar, salt, and oregano. Massage and mix the onions well so they soften and soak up the flavor.
Add the chopped potatoes to a large serving bowl along with the tomatoes, Kalamata olives, basil, parsley, capers if using, crushed red pepper flakes, and the marinated onions with all the vinegar mixture.
Pour in the extra virgin olive oil and gently toss everything together until evenly coated.
Taste and adjust with additional salt, pepper, olive oil, or crushed red pepper flakes as needed.
Let the potato salad sit for at least 20–30 minutes before serving so the flavors can blend together.
Serve at room temperature or chilled.
