Place the spinach in the bottom of a 1 1/2 qt buttered casserole. I usually have to cook the chicken while I get everything else ready - I just add some olive oil to a pan and cook it up on the stove, then cut it into chunks with my kitchen shears. You could also buy the precooked chicken in the grocery store; Tyson makes some that is good.
Melt the margarine in a saucepan and stir in the flour. Let bubble one minute, stirring constantly.
Add spices and milk. Stir constantly until mixture thickens; add cheese and chicken.
Pour chicken mixture over spinach. Top with bread crumbs and dot with butter.
Bake at 350 degrees for 20 minutes or until casserole is heated completely. If bread crumbs need additional browning, place under the broiler for a minute or two.