01 - Preheat oven to 375°F. 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 cook until translucent, about 3–4 minutes. Stir in the minced garlic and cook for 1 minute until fragrant.
03 - Add spinach to the skillet. If using fresh spinach, sauté until wilted; if using frozen, cook until heated through. Remove from heat.
04 - Transfer the cooked vegetables to a large mixing bowl. Add the shredded chicken and chopped artichoke hearts, stirring to combine evenly.
05 - In a separate bowl, combine the Greek yogurt, cream cheese, cottage cheese, half of the mozzarella, Parmesan, Italian herbs, salt, black pepper, and cayenne pepper. Mix until smooth and well blended.
06 - Fold the cheese mixture into the chicken and vegetable mixture, stirring thoroughly until everything is evenly coated.
07 - Spoon the mixture into the prepared casserole dish, spreading it into an even layer. Top with the remaining mozzarella and gluten-free breadcrumbs if using.
08 - Bake for 25–30 minutes, or until the casserole is bubbly and the top is golden brown.
09 - Remove from the oven and let rest for 5–10 minutes before serving to allow the casserole to set.