Preheat oven to 350º F.
In large bowl, beat together mayonnaise, flour, eggs, milk, salt and pepper.
Fold in catfish, cheese and onions. Pour into pie crust. Bake in middle of oven for 40 minutes, or until a knife inserted near the center comes out clean.
Cool on wire rack 5 minutes before serving. Garnish with thinly sliced green onions if desired.