Heat oven to 350 F.

Melt butter in a medium skillet over medium-high heat.

Add onion and poppy seed and saute until the onion just starts to soften. Remove from heat.

Cut the rolls in half, horizontally, keeping the top and bottom halves in tact. Just lay them out on a flat surface and run your knife through the middle, parallel to the ground.

Spray a 9" x 13" baking dish with non-stick spray.

Spoon 1/3rd of the onion mixture over the bottom of the dish.

Add the bottom half of the rolls. Top with ham and cheese.

Add the bun tops.

Spoon remaining onion mixture over the buns.

Bake for 15-20 minutes.

Use a sharp knife to separate the buns, cutting through the cheese and ham.