Crawfish Fettuccini

1 cup butter
1 onion, chopped
1 green bell pepper, chopped
1 cup diced celery
3 cloves garlic, minced
2 tablespoons all-purpose flour
1 teaspoon Cajun seasoning
1 cup milk
1 (10.75-ounce) can cream of mushroom soup
8 ounces processed cheese with jalapenos, cubed
2 (16-ounce) packages frozen cooked, peeled, and deveined crawfish tails, thawed
1 (16-ounce) package fettuccini, cooked and kept warm
Garnish: fresh chopped green onions

In a large skillet, melt butter over meduim heat. Add onion, bell pepper, celery, and garlic; cook for 5 minutes, or until tender. Add flour and Cajun seasoning; cook for 2 minutes, stirring frequently. Stir in milk; cook for 5 to 6 minutes, or until slightly thickened, stirring constantly. Add soup and cheese, stirring until cheese is melted. Add crawfish, and cook until warmed through. Serve over fettuccini. Garnish with green onions, if desired.