Cook chicken as desired until no longer pink (or use leftovers if you have some on hand); shred or cut into bite-sized pieces.
Finely dice carrots, potatoes, celery, onion, and mushrooms. In a soup pot, heat a small drizzle of olive oil over medium heat. Add veggies to the pan and cook over medium heat until crisp-tender.
Add garlic, rosemary, and sage, and cook 1-2 minute longer until fragrant.
Pour in 3 cups of the chicken stock and add the cooked chicken. Bring mixture to a simmer over medium heat and let simmer 15-20 minutes until vegetables are completely tender.
While the soup is simmering, make the roux. In a small saucepan, stir together flour and olive oil (it will be a thick paste). Cook 1-2 minutes over medium heat, stirring constantly. Stir in remaining 1 cup of the chicken broth and bring to a simmer; mixture will begin to thicken.
Pour roux into the soup pot with the chicken and vegetable mixture. Continue to simmer another 5-10 minutes until the soup has thickened slightly. Add salt and pepper to taste.
If soup is too thick, add additional stock as desired.
Serve with a side of oranges.