Heat oil in large pot. Add sausage and saute until browned on all sides. Remove sausage from pan with a slotted spoon; drain on paper towels. Add chicken pieces; sauté 4 minutes until lightly browned on all sides. Add onion, bell pepper, celery, Cajun seasoning and garlic; sauté for 4-5 minutes or until vegetables are tender, stirring occasionally. Add stock and tomatoes; bring to a boil. Return sausage to pan; reduce heat to medium-low, and simmer 6 minutes, stirring occasionally. Serve over steamed brown rice.