Heat the oil in a nonstick medium skillet. Add the onions, season with 1/4 teaspoon kosher salt and cook over low heat, stirring frequently, until caramelized, 25 minutes; set aside.
Preheat the oven to 350 degrees F.
In a large mixing bowl, beat the cream cheese with a hand-held electric mixer until smooth; beat in the mayonnaise until smooth. Add the reserved caramelized onions, the artichoke hearts, mozzarella, Parmesan, hot sauce, Worcestershire and half of the green onions. Add an additional 1/4 teaspoon of salt and some black pepper to taste and stir together until combined. Transfer the dip to a pie plate or shallow gratin dish and bake until the top is golden brown, 30 to 40 minutes.
Serve hot with crackers, tortilla chips, crostini or veggies. Garnish with the remaining green onions.