Heat butter in pan and saute onions until brown. Remove onions from pan and add chicken. Saute until brown on all sides. Add peppers and tarragon. Cook for 1 minute. Stir in tomatoes and return onions to the pan. Add salt and pepper. Cover and simmer for 20 minutes. Heat reserved stock in separate saucepan. Remove chicken from pan and set on plate. Stir in bulgur and combine with the vegetables. Simmer for 3 minutes. Add the hot chicken stock, let boil 1 minute. Cover and simmer for 15 minutes. Add chicken and allow to warm. Remove from heat and serve.