Preheat the oven to 400 degrees F. In a large saute pan, heat the oil until it begins to ripple. Add the potatoes, cooking and tossing until they are all golden. Add the tomatoes and onions and cook for 2 minutes. Add the garlic and oregano, toss to combine. Season with the salt and pepper. Top with the feta and place in the oven for 10 minutes.