1. Preheat the oven to 350 degrees F. Grease a 9x13 baking dish with cooking spray and set aside.
2. Add quinoa and water to a medium saucepan and bring to a boil over medium heat. Boil for 5 minutes. Turn the heat to low and simmer for about 15 minutes, or until water is absorbed. Remove from heat and fluff with a fork. Set aside.
3. In a large skillet, heat the olive oil over medium-high heat. Add the onion and garlic. Sauté until softened, about 5 minutes. Add spinach and cook until it shrinks down, about 3 minutes. Stir in the artichoke hearts. Season with salt and pepper, to taste. Turn off the heat and set aside.
4. In a medium saucepan add 3 tablespoons of butter and flour and heat over medium heat. Whisk continuously until a paste forms. Whisk in milk. Increase heat to medium/high and bring to a boil whisking the whole time. Stir in cream cheese and 1/2 cup of the shredded mozzarella cheese. Whisk until smooth.
5. In a large bowl, combine quinoa, spinach and artichoke mixture, and cheese sauce. Stir well. Stir in the remaining 1 cup of shredded mozzarella cheese. Pour mixture into prepared baking dish. Top with feta cheese.
6. To make the topping, combine melted butter, Panko bread crumbs, and Parmesan cheese in a small bowl. Sprinkle over the quinoa bake. Cover the pan with aluminum foil.
7. Bake for 20 minutes. Remove foil from pan. Cook for another 15-20 minutes, or until the quinoa bake top is golden brown and slightly bubbling. Serve warm.