Preheat oven to 325 degrees F (165 degrees C).
In a small mixing bowl, combine onion flakes, mustard, poppy seeds and butter.
Split each dinner roll. Make a sandwich of the ham and cheese and the dinner rolls. Arrange the sandwiches on a baking sheet. Drizzle the poppy seed mixture over the sandwiches.
Bake for 20 minutes, or until cheese has melted. Serve these sandwiches warm.