Preheat oven to 375 degrees F. Spray a 9 x 13″ baking dish with cooking spray and set aside.
Heat butter or oil in a skillet over medium-high heat. Add onion and chicken, and lightly sprinkle with seasoned salt. Cook and stir until chicken is cooked through.
While chicken cooks, heat frozen quinoa and vegetables in microwave according to package directions. (If making quinoa for this recipe, start it cooking in step one of this recipe according to package directions.)
In a large bowl, stir together chicken and onions, quinoa, vegetables, soup, milk, and one cup of cheddar cheese. Transfer mixture into prepared baking dish, and bake uncovered in preheated oven for 20 minutes.
Carefully sprinkle remaining cheese over the top of the casserole, and spread the crushed chips over the cheese. Bake an additional 10 minutes or until cheese is melted and bubbly. Serve and enjoy!