In a medium bowl, combine mayonnaise and cream cheese, mixing until blended and creamy. Add chopped artichoke hearts, drained spinach and grated Parmesan cheese. Mix well and stir in minced garlic and lemon juice. Spread mixture evenly into prepared baking dish. Cover with aluminum foil and bake in oven for 20 minutes. Remove foil for final 5 minutes of baking time.
Serve with bread cubes, crackers or tortilla chips for dipping.