Split croissants open with a serrated knife. Top each half of each croissant with 1 teaspoon of butter & 1 teaspoon of Dijon mustard.
Then top each bottom half with 1 Swiss cheese slice, a slice of ham, and 1 Provolone cheese slice (folding ham and cheese to fit, if needed).
Place stuffed croissants in a single layer on a lightly greased (with cooking spray) 9 x 13-inch baking dish.
Bake at 375 degrees F for about 15 minutes.
Remove from oven and brush tops of croissants with melted butter. Sprinkle them all with the Everything Bagel Seasoning. Serve warm with pickled red onions.