In a large saucepan, cook cauliflower in a small amount of water for 6-7 minutes or until crisp-tender; drain well. In a medium saucepan, saute onion in butter for 2 minutes. Stir in flour until blended; gradually add milk. Bring to a boil; boil for 2 minutes, stirring constantly.
Remove from the heat; stir in cheese until melted. Add salt, garlic salt and pepper. Place half of the cauliflower in a greased 2-1/2-qt. baking dish; top with half of the sauce. Repeat.
Bake, uncovered, at 350° for 20 minutes or until bubbly. Add olives for eyes and mouth and a carrot for the nose.