01 - Preheat oven to 375°F. Lightly grease a 9x13-inch casserole dish with cooking spray or butter.
02 - Heat olive oil in a large skillet over medium heat. Sauté the diced onion until softened and translucent, about 4 minutes. Add the minced garlic and cook for an additional 1 minute until fragrant.
03 - Add the chopped spinach to the skillet and cook, stirring occasionally, until wilted if using fresh, or heated through if using frozen. Remove the skillet from heat and set aside.
04 - In a large mixing bowl, combine the softened cream cheese, sour cream, chicken broth, salt, black pepper, and dried Italian herbs. Stir until smooth and well blended.
05 - Fold the shredded chicken, chopped artichoke hearts, spinach mixture, half of the mozzarella cheese, and half of the Parmesan cheese into the cream base. Mix until everything is evenly distributed.
06 - Transfer the mixture to the prepared casserole dish, spreading it out in an even layer. Top with the remaining mozzarella and Parmesan cheeses, then sprinkle the gluten-free breadcrumbs evenly over the surface.
07 - Bake uncovered for 25 to 30 minutes, or until the casserole is bubbly around the edges and the top is golden brown.
08 - Remove from the oven and let the casserole rest for 5 minutes before serving to allow it to set.