Heat the oil in a saute pan over medium heat. Add onions and cook, stirring occasionally, 4 to 5 minutes. Add garlic and cook an additional 3 to 4 minutes, or until onions are light-golden but not browned. Remove from heat and cool.
In the bowl of a food processor combine the artichoke hearts, spinach, sour cream, mayonnaise, Neufchatel, mozzarella and salt and pepper. Process until smooth. Fold vegetable puree into sauteed onions, then spread into an 8-inch glass square baking dish or 9-inch glass pie plate which has been lightly sprayed with cooking spray. Bake for 25 to 30 minutes or until heated through. Serve with pita wedges or crudites.