1) Preheat the oven to 190C/Gas 5.
2) Heat the oil in a saute pan over medium heat. Add the onions and cook, stirring occasionally, for 4 to 5 minutes. Add the garlic and cook for an additional 3 to 4 minutes, or until the onions are light golden but not browned. Remove from the heat and cool.
3) In the bowl of a food processor, combine the artichoke hearts, spinach, sour cream, mayonnaise, Neufchatel, mozzarella and salt and pepper. Process until smooth. Add the cooled onion-garlic mixture to the food processor and pulse a few times to combine.
4) Transfer the mixture into an 20cm glass square baking dish or 23cm glass tart dish which has been lightly sprayed with cooking spray. Bake for 15 to 20 minutes or until heated through.
Serve with pita wedges or crudites.