Add the onions to a foil-lined baking sheet, drizzle with olive oil and sprinkle with salt and pepper. Toss everything together. Transfer to the oven and roast for 35 minutes, or until the onions are tender and golden. Set aside to cool completely.
In a stand mixer fitted with a paddle attachment, combine the cream cheese, sour cream, Parmesan, mayonnaise, Worcestershire, chives and the roasted onions. Beat until light and fluffy and well-combined. Scrape the mixture into a serving bowl using a rubber spatula. Sprinkle the remaining chives over the top and serve.