Preheat your oven to 375°F (190°C). Lightly grease a medium-sized baking dish (an 8x8 inch square dish or a small 1-quart casserole dish works well).

Prepare the vegetables: Ensure the frozen spinach is fully thawed. Using a clean kitchen towel or paper towels, squeeze the spinach vigorously until all excess moisture is removed. This step is crucial to prevent a watery dip.

Drain the artichoke hearts and roughly chop them into small, manageable pieces.

In a large mixing bowl, combine the softened cream cheese, sour cream, and mayonnaise. Use a hand mixer or a sturdy spoon to beat the mixture until it is smooth and uniform.

Add the minced garlic, onion powder, black pepper, salt, and red pepper flakes (if using) to the cream cheese mixture. Stir thoroughly to distribute the seasonings evenly.

Add the squeezed, dry spinach and the chopped artichoke hearts to the creamy base.

Fold in the Parmesan cheese, Monterey Jack cheese (if using), and 3/4 cup of the shredded Mozzarella cheese. Reserve the remaining 1/4 cup of Mozzarella for the topping. Stir gently until everything is evenly combined.

Spoon the prepared dip mixture into the lightly greased baking dish, spreading it out into an even layer. Sprinkle the reserved 1/4 cup of Mozzarella cheese over the top.

Bake for 20 to 25 minutes, or until the edges are bubbling and the topping is golden brown and melted.

Remove the dip from the oven and allow it to cool for 5 to 10 minutes before serving. Serve hot with tortilla chips, pita chips, crostini, or slices of crusty bread.