In a dutch oven (or large pot), heat oil over medium-high then add sausage, carrots, celery, onions and red pepper and cook until sausage is browned and veggies are slightly softened (about 5 minutes). Sprinkle in flour and add garlic then cook for an additional 3 minutes, stirring to combine flour with the remaining oil.
Add chicken broth, tomatoes and Cajun seasoning then simmer for 20 min.
Add shrimp and bay scallops 6-8 min before serving so as not to over cook. *Be sure seafood is fully cooked before serving.
Serve gumbo hot, over cooked rice.
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Notes
Be careful not to overcook the seafood or it will become rubbery. Once soup is cooked, serve immediately or chill and heat right before serving.