Heat the oil and flour in a heavy-duty skillet (i.e., cast-iron) over medium-low heat. Whisk continuously until a dark roux has form, about 15 to 25 minutes. Remove from heat.
Carefully, to the roux, add the onions, celery, bell pepper, garlic, poblano, jalapeno, and parsley. Stir until well coated and slightly softened about 2 minutes.
Add the roux/veggie mixture to the heated seafood stock in a large pot, preferably a Dutch oven. Stir in the peppers, paprika, thyme, salt, and bay leaves. Bring to a simmer and stir frequently. The etouffee will begin to thicken as you stir.
Meanwhile, melt the butter in a large skillet. Add the crawfish (or shrimp) and green onions and cook for 5 minutes, stirring occasionally.
Transfer the crawfish mixture to the large pot along with the lemon juice and simmer for another 5 minutes.
Serve warm over steamed white rice and garnish with chopped green onions. Passing cayenne hot sauce at the table.