Preheat oven to 375
Bring chicken stock to a boil in a small saucepan. Add quinoa, then cover and reduce heat to low for about 15 minutes. Turn heat off and allow to sit for 5 minutes, then fluff up and set aside.
Make the sauce. Combine 2 cups diced tomatoes, tomato paste and balsamic vinegar over medium heat. Add whipping cream, crushed red pepper flakes and salt/pepper and continue cooking until heated through.
In a large bowl, mix the chicken, quinoa, Parmesan cheese, 1/2 cup mozzarella and mushrooms. Add the sauce and mix again.
Pour this mixture into a prepared 9x13 baking dish and top with remaining mozzarella and diced tomatoes.
Bake for about 15 minutes, or until heated through and cheese is melted.