In a large skillet, melt the butter. Sauté the garlic over moderate heat until fragrant, about 30 seconds. Add the onion, celery and bell pepper and cook, stirring occasionally, until tender and translucent, about 5 minutes. Stir in the cream of mushroom soup and cheese until smooth and melted. Add the crawfish tails and cook over low heat, stirring occasionally, until heated through, about 2 minutes.