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. Add the diced onion and sauté until softened and translucent, about 4 minutes. Add the minced garlic and cook for an additional 1 minute until fragrant.
03 - Stir in the chopped spinach and cook 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, and half of the mozzarella and Parmesan cheeses into the cream base. Mix until all ingredients are evenly distributed.
06 - Transfer the mixture into the prepared casserole dish, spreading it out evenly. Top with the remaining mozzarella and Parmesan cheeses, then sprinkle the breadcrumbs over the surface.
07 - Bake uncovered for 25 to 30 minutes, or until the casserole is bubbly and the top is golden brown.
08 - Remove from the oven and let the casserole rest for 5 minutes before serving to allow the filling to set.