01 - Preheat the oven to 400°F. Lightly grease a large baking dish or sheet pan.
02 - In a large bowl, toss the halved potatoes and red onion with olive oil, lemon zest and juice, garlic, oregano, black pepper, chili flakes if using, and salt until evenly coated.
03 - Spread the potato mixture evenly in the prepared baking dish.
04 - Scatter the feta cubes over the potatoes.
05 - Bake for 35–40 minutes, stirring once halfway through, until the potatoes are tender and golden brown and the feta is slightly browned.
06 - Remove from the oven, sprinkle with fresh parsley, and serve warm.