Preheat your oven to 350°F (175°C).

In a large mixing bowl, combine the thawed and drained spinach, chopped artichoke hearts, softened cream cheese, sour cream, grated Parmesan cheese, shredded mozzarella cheese, mayonnaise, minced garlic, salt, black pepper, and optional red pepper flakes. Mix until well blended.

Gently fold in the shredded cooked chicken.

Lightly grease a baking dish and transfer the mixture into the dish, spreading it evenly.

Bake for 25-30 minutes until the top is golden brown.

Remove from the oven and let it cool for a few minutes before serving.