Cook brown rice in water and chicken bouillon according to package directions.
While the rice is cooking, in a large heavy saute pan cook chicken sausage on medium heat, breaking up the meat into small pieces as it cooks until the sausage is cooked through and is browned. Set aside on a dish.
Add olive oil to the pan and add the onion, sauté one minute, add the celery, salt and pepper to taste; cook about 12 minutes, until celery is soft.
Add the mushrooms to the pan, more salt and pepper if needed and cook, stirring 5 minutes, then cook covered for 2 minutes, or until the mushrooms have released their juice and are cooked through.
Add the sausage and the cooked rice to the pan and mix well.