Preheat oven to 375 degrees F. Spray large 9 x 13 baking dish with cooking spray. Set aside.

In a medium bowl, whisk the eggs. Add cooked quinoa, cheese and pepper; stir with a spoon to combine and set aside.

In another medium bowl, make the slurry by combining chicken stock, milk, cornstarch and whisk with a fork. Make sure liquids are cold otherwise cornstarch will lump.

Preheat large ceramic non-stick skillet on medium heat and swirl oil to coat. Add onion and celery; cook for 5 minutes, stirring occasionally. Add mushrooms and cook for 3 more minutes.

Add thyme, garlic powder, salt, pepper, peas, corn and carrots. Cook for 3 minutes, stirring occasionally.

Whisk the slurry again (cornstarch settle to the bottom quickly) and add to the skillet. Bring to a boil and cook until filling bubbles and thickens. Add cooked chicken and stir to combine. Turn off heat.

Transfer filling to prepared baking dish and flatten with a spatula.

Drop spoonfuls of quinoa mixture on top and spread with a spatula to cover the filling evenly.

Bake uncovered for 25 minutes.

Remove from the oven, let cool for 5 - 10 minutes and cut into 8 squares. Serve hot.