Place rack in center of oven then preheat to 425 degrees. Coat a 9" x 13" baking dish with cooking spray then place quinoa in the baking dish, spreading the grains into an even layer. Bake quinoa for 8–10 minutes, stirring once or twice, just to dry it out and toast it slightly. Remove from oven then break up any clumps that may have formed. Set aside to cool.
Rinse chicken under cool water then pat dry with paper towels then season on both sides using salt, pepper and ½ tsp of garlic powder.
Gather three separate plates then place flour (or gluten-free flour) on one plate, the beaten eggs on the second plate and toasted quinoa on the third. Wipe out the baking dish using a towel then re-coat with cooking spray. Dredge each chicken breast in the flour then dip in beaten egg. Allow as much egg to drain off of the chicken as possible then encrust the chicken completely with quinoa. Place the chicken into the baking dish and sprinkle each breast with 1 Tbsp of Parmesan cheese.
Bake 15 minutes, then remove from oven. Pour marinara sauce over chicken then sprinkle with mozzarella cheese. Return baking dish to the oven for an additional 8–10 minutes—or until the chicken is cooked through, cheese is melted and sauce is hot and bubbly. Remove from oven, sprinkle with parsley then let the dish rest for 5 minutes before serving. Enjoy!
If you are gluten-free, I suggest shredding your own cheese. Sometimes pre-shredded, packaged cheese contains starch to prevent clumping—which contains gluten!