Preheat oven to 350 degrees F. Coat a square 9x9 inch casserole dish with cooking spray.
In a medium sauce pan, combine raw quinoa, salt, onion powder and chicken broth. Bring the quinoa to a boil, then reduce heat to a simmer.
Cover and cook for approximately 15 minutes, or until cooked. When the quinoa is cooked, all of the liquid will be absorbed. Remove from heat and fluff with a fork.
In a medium mixing bowl, combine eggs, milk, pepper, garlic and 1 1/2 cups shredded cheddar cheese. Mix until combined.
Add quinoa and broccoli, mix until combined. Transfer to prepared casserole dish. Bake, uncovered, for 40 minutes. Remove and top with remaining 1/2 cup cheddar cheese. Return to oven for 4-5 minutes or until cheese has melted. Allow to sit for 5 minutes before serving. Garnish with green onions, optional.