Preheat your oven to 350°F (175°C).
In a skillet, heat olive oil over medium heat. Add minced garlic and fresh spinach, cooking until the spinach is wilted.
In a large bowl, combine shredded chicken, sautéed spinach, artichoke hearts, Greek yogurt, mozzarella cheese, Parmesan cheese, oregano, onion powder, salt, and black pepper until well mixed.
Grease a baking dish with cooking spray or olive oil. Pour the mixture into the dish and spread it evenly.
If desired, sprinkle breadcrumbs over the top for added texture and crunch.
Place the casserole in the preheated oven and bake for about 30-35 minutes until the top is golden brown.
Once baked, allow the casserole to cool for a few minutes before serving.