melt the butter in a saucepan and stir in the flour, garlic powder, salt and pepper. add the milk and stir until it begins to thicken. add the cheese and stir until it's smooth. layer the potatoes, onion, ham and cauliflower in a greased 9 x 13 baking dish. pour the cheese sauce over the top. cover with foil and bake at 375o for 1 hour.
Remove the foil and sprinkle the crushed cereal over the top and bake for 10-15 more minutes or until it's bubbly and lightly browned. Let it sit about 10 minutes before serving.