Spread quinoa in a thin layer on a rimmed baking sheet; bake at 325°F until browned, about 30 minutes, stirring every 10 minutes.
Heat a large stockpot over medium. Add oil. Add onion, carrot, bell pepper, and garlic; cover and cook 10 minutes or until vegetables are tender, stirring occasionally. Uncover and stir in rosemary and cumin; cook 1 minute, stirring constantly. Stir in stock, potatoes, celery root, and toasted quinoa. Increase heat to high; bring to a boil. Cover and reduce heat to medium; cook 12 minutes. Stir in zucchini and Brussels sprouts; cook until vegetables and quinoa are tender, about 2 minutes. Stir in parsley and salt.
