Preheat the oven to 355 degrees F.
Slice each croissant in half and place the bottom halves tightly together in an 9 x 13 inch oven safe dish.
Spread some of the mustard on each of the croissant bases and top with 8 slices of swiss cheese.
Fold each slice of ham and place on top of each croissant followed by the remaining 8 slices of cheese on top.
Combine the poppy seeds, onion, garlic and sesame seeds in a bowl and stir to mix well.
Place the top halves of each croissant on top and brush with some melted butter.
Sprinkle the everything seed mixture liberally on top of the croissants.
Place in the oven and bake for about 25 minutes and golden brown on top.
Slice the croissants into 10 and serve at once.