Place the tail meat in a bowl, sprinkle with creole seasoning and set aside.
Place 8 cups of crawfish stock in a stock pot and warm until almost boiling.
Heat the vegetable oil in a large cast iron dutch oven over high heat.
When the oil is shimmering, add the flour and whisk constantly until you have a medium roux. Add the trinity (yellow onions, celery and bell peppers) into the roux and stir constantly until softened, about 8 minutes.
Add the garlic, about ⅔ of the green onions and the creole seasoning. Stir until blended and becoming aromatic, about 2 minutes.
Add the crawfish tails in about four batches and the tomato sauce, stir to mix well.
Making sure the stock is about the same temperature as the roux mixture, slowly add stock to the roux and crawfish, a ladle at a time, stirring to completely blend the stock into the roux mixture before adding the next ladle.
Continue this, one ladle at a time, until about half of the stock has been added, then you can add the balance of the stock and mix together very well. Make sure there are no lumps.
Bring the bisque to a high boil, reduce heat to a medium simmer and let it simmer for about 15 minutes uncovered.
Add the stuffed crawfish heads and return to a boil.
Once it boils, lower the heat to a simmer, cover and continue to simmer for about 45 minutes to 1 hour. Stir often to keep the heads off the bottom of the pot.
Add some of the reserved stock if it gets too thick.
After 45 minutes add the parsley and stir well.
Serve in a bowl over a scoop of white rice, making sure to get some of the stuffed heads in each serving. Sprinkle chopped green onions on top.