Place the potatoes in a large pot and cover with cold water by about 1 inch (2.5 cm). Salt the water generously and bring it to a boil over high heat.
Reduce the heat to maintain a steady simmer. Cook until the potatoes are fork-tender but still hold their shape, about 12 to 15 minutes. Drain well and let them steam dry in the colander for 2 minutes.
While the potatoes cook, stir the parsley, oregano, garlic, red onion, olive oil, red wine vinegar, red pepper flakes, salt, and black pepper together in a large serving bowl.
Add the warm drained potatoes to the chimichurri. Fold gently until every piece is coated, taking care not to break up the potatoes.
Taste and add more salt, pepper, vinegar, or red pepper flakes if needed. Serve warm, at room temperature, or chilled.