Heat the oil and flour in a skillet over medium heat, whisking constantly for about 5-10 minutes. The roux should be a light brown color.
Add the onions, green peppers and celery and mix to coat with the roux.
Add the spices and Worcestershire sauce and stir together.
Slowly pour in the stock while whisking constantly (to avoid clumps). If mixture is too thick, continue adding stock while whisking until it resembles a very thick stew.
Simmer for 10 minutes.
Add the crawfish tails, cook 1-2 minutes, until heated through and remove from heat.
Serve with steamed white rice, green onions and Louisiana hot sauce (optional).
Notes
Add additional Cajun seasoning for more flavor.
Amp up the spice factor by adding ¼ to ½ teaspoon of cayenne pepper or using hot paprika instead of regular.
ALWAYS watch the roux while cooking it. It can burn quickly then you have to start over again. It should be a golden brown when done.
Substitute shrimp for the crawfish tails if you can't find them. You can also use chicken or fish.
You can also use seafood stock instead of chicken if you prefer a more seafood forward flavor.