Place the crawfish tails, chopped onion, bell pepper, celery, garlic, stale bread, and egg into the bowl of a food processor. Add the salt, black pepper, and 2 teaspoons of Cajun seasoning. Cover and pulse until the crayfish mixture is finely chopped. Scrape into a bowl and fold in the parsley and green onions. Cover and refrigerate 1 hour.
Heat oil in a deep-fryer or large saucepan to 350 degrees F (175 degrees C). Whisk the bread crumbs and 1 tablespoon of Cajun seasoning together in a bowl; set aside.
Form the crawfish mixture into 1 tablespoon-size balls and roll in the bread crumbs. Cook in batches in the hot oil until the balls turn golden brown and begin to float, about 4 minutes. Drain on a paper towel-lined plate and serve hot.
