Peel, devein and rinse shrimp. Pat dry with paper towel, sprinkle with creole seasoning and set aside.
Heat oil in a cast iron or other heavy dutch oven. When nearly smoking, add flour and make a dark roux.
Add yellow onions, green peppers, celery and green onions, stirring often until cooked down and coated with the roux, this will take 10 to 15 minutes.
Add the garlic and stir until aromatic-about 2 minutes.
Add about ⅔s of the Herb and Spice Blend, reserve the remainder.
Add the okra and combine well with the roux/veggie mixture.
Simmer about 10 to 15 minutes, add parsley and a little more of the seasoning mix. (Continue to simmer an additional 10 to 15 minutes if the okra is excessively slimy) Let this sit until the stock is at a rolling boil.
In a separate stock pot, bring the stock to a rolling boil.
Using a slotted spoon, add the veggie mix one spoonful at a time, stirring well until each spoonful is dissolved. Bringing the stock back to a rolling boil between each spoonful, repeat this process until all the veggies are mixed in the stock. Once all the veggies/roux have been mixed into the stock, bring it to a rolling boil for 10 minutes
Lower heat, cover pot and simmer for 30 minutes, stirring occasionally so it does not stick
Uncover pot and bring back to a boil. Add the shrimp a few at a time by hand. When all shrimp have been added, stir well and lower to a simmer, cover and cook about 5 minutes.
Add the remainder of the Herb and Spice Blend and the parsley. Add the crab meat (if using), stir well, return to a simmer for about 5 minutes, covered.
Turn off heat, taste for seasoning and adjust as needed. Let the gumbo sit covered for about 10 minutes then skim any grease off the top and serve over rice.