Melt the butter in a large, heavy skillet over medium heat, and stir in the onion, green bell pepper, green onions, and celery; cook the vegetables, stirring frequently, until the onion is translucent and the vegetables have begun to soften, about 10 minutes. Stir in the golden mushroom soup, parsley, Cajun seasoning, salt, and black pepper, and bring the sauce to a boil.

Gently mix in the crawfish tail meat, and simmer until the crawfish tails are opaque, 10 to 15 minutes.