Preheat oven to 400˚F. Heat oil in large skillet set over medium heat; cook spinach for about 3 minutes or until wilted. Let cool completely. Squeeze out excess moisture and chop finely.
Combine mozzarella, Parmesan and Asiago cheese; reserve 1/4 cup and set aside. Using electric mixer, beat cream cheese until light and fluffy. Add yogurt, lemon zest, lemon juice, garlic, salt, pepper, cayenne (if desired), and remaining cheese mixture; beat until blended. Stir in spinach and artichokes.
Scrape into greased 4-cup baking dish. Sprinkle with reserved cheese mixture. Place on baking sheet; bake for about 15 minutes or until heated through and top is golden brown and melted. Serve warm with crackers.
Tip: For make-ahead, assemble dip, then cover and refrigerate. Bake just before serving & serve warm.