Make a roux by stirring the flour and vegetable oil together in a havy pot over medium-low heat until a well-browned panut butter color, not burned.
When roux is made, add onions, bell pepers, celery and garlic. Cook, stirring until vegetables are limp, being careful not to burn.
Add tomatoes, tomato sauce, salt and pepper. Cook and stir until well blended.
Add water and cook 50 minutes.
Turn fire off. Let sit until ready to serve.
Just before serving, bring to a light bubble. If too thick, add more water. Add shrimp. Cook 10 minutes.
Add parsley, green onions, oysters and crabmeat. Cook 5 minutes more.
NOTE: It is important not to overcook the seafood. Serve immediately.