Heat the olive oil in a medium skillet over medium-high heat. Add the onion and saute until beginning to brown, 5 to 7 minutes. Stir in 1/4 cup water and scrape up any browned bits from the bottom of the pan. Turn the heat to low and cook until the onion is golden brown, 30 to 35 minutes, stirring occasionally. If the pan ever looks too dry, add a tablespoon of water. Let cool completely.
Combine the cream cheese, mayonnaise, sour cream, Worcestershire sauce, garlic salt, onion powder and 1/2 teaspoon pepper in a medium bowl and beat with a mixer until smooth. Stir in the caramelized onion and the scallion. Chill until serving time. Top with more scallions and serve with vegetables for dipping.