In a medium pot, sauté onions, carrots, and celery in ¼ cup water or vegetable broth until slightly browned, approximately 5 minutes. Add wild rice, brown rice, mushrooms, poultry seasoning, sage, black pepper, and remaining water or vegetable broth. Bring to a boil on medium-high heat and then simmer on medium-low heat for 30-40 minutes or until all liquid is absorbed. Add walnuts and parsley and cook for 2 more minutes. Remove from heat.