01 - Preheat the oven to 400°F. Lightly grease a large baking dish or sheet pan with cooking spray or a small amount of olive oil.
02 - In a large mixing bowl, combine the halved baby potatoes and red onion wedges. Pour in the olive oil, then add the lemon zest, lemon juice, minced garlic, dried oregano, black pepper, chili flakes if using, and salt to taste. Toss everything together until the potatoes and onions are evenly coated with the seasoning mixture.
03 - Spread the seasoned potato and onion mixture evenly across the prepared baking dish, ensuring the vegetables are in a single layer for even roasting.
04 - Scatter the cubed feta cheese over the top of the potato mixture, distributing the pieces evenly throughout the dish.
05 - Place the baking dish in the preheated oven and bake for 35 to 40 minutes. About halfway through the cooking time, stir the mixture gently to promote even browning. Continue baking until the potatoes are fork-tender and golden brown, and the feta has softened and developed light golden edges.
06 - Remove the dish from the oven and immediately sprinkle with fresh chopped parsley. Allow to cool for a few minutes before serving warm as a vibrant Mediterranean-inspired side dish.