Add the olive oil, garlic, and onion to a skillet. Cook over medium heat 5-10 minutes, until the onion is softened
Add the artichoke hearts, frozen spinach, cream cheese, sour cream, mayo, and parmesan cheese to a saucepan or dutch oven and stir over medium heat until melted and creamy
Stir in the garlic and onion into the dip mixture once cooked
Salt to taste (I used ½ teaspoon)
Transfer the spinach artichoke dip mixture to a greased small baking dish
Top with the mozzarella cheese
Bake the dip at 375 degrees for 15-20 minutes, until hot and bubbly.
Optional: broil 1-2 minutes at the end to get the top browned. If you do this, watch closely to avoid burning