In a skillet, heat butter or margarine and
saute onions for 5 minutes.
Stir in croutons and saute
for another 3-4 minutes.
In a greased 2 quart casserole,
layer crouton-onion mixture,
tomatoes, sprinkle with basil and
salt and pepper, then cheese.
End with tomatoes and cheese.
Bake in preheated 350 oven for 35-40 minutes
or until cheese is melted.
NOTE: You can use flavored croutons also.