Place 2 cups water and quinoa in a large saucepan, then bring to a low boil. Reduce heat to low, cover, and let cook for 15 minutes. Remove from heat and let stand, still covered, for 5 minutes. Fluff with a fork and set aside.
Preheat oven to 350 degrees F. Coat a large casserole dish (9x13-inch or similar) with cooking spray and set aside.