01 - Preheat oven to 375°F. Grease a 9x13 inch casserole dish with cooking spray or butter.
02 - In a large skillet, heat olive oil over medium heat. Add diced onion and cook until translucent, about 3–4 minutes. Add minced garlic and cook for 1 minute until fragrant.
03 - Add spinach to the skillet. Sauté until wilted if using fresh, or until heated through if using frozen. Remove from heat.
04 - Transfer the cooked vegetables to a large mixing bowl. Add the shredded chicken and chopped artichoke hearts, then stir to combine evenly.
05 - In a separate bowl, combine Greek yogurt, cream cheese, cottage cheese, half the mozzarella, Parmesan, Italian herbs, salt, pepper, and cayenne. 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 golden brown on top.
09 - Remove from the oven and let rest for 5–10 minutes before serving to allow the filling to set.