Microwave cauliflower on high for 4 minutes. Arrange flowerets in a greased 1 ½ quart casserole dish. Heat margarine over low heat; blend in four. Gradually add milk; cook over low heat until thickened; stirring constantly. Add cheese; stir until melted. Add celery, salt, pepper and drained tuna. Pour over cauliflower; sprinkle with additional grated cheese and dust with paprika. Freeze.