Preheat the oven to 375°F (190°C).
Line a baking sheet with parchment paper or lightly grease it.
In a small bowl, whisk together the Dijon mustard, honey, buffalo sauce, melted butter, garlic powder, smoked paprika, and black pepper.
Slice each croissant in half horizontally without cutting all the way through.
Spread a generous layer of the buffalo honey mustard sauce inside each croissant.
Layer one slice of Swiss cheese, two slices of ham, and one slice of cheddar cheese inside each croissant.
Arrange the filled croissants on the prepared baking sheet.
Brush the tops with a little of the remaining sauce.
Sprinkle the mozzarella and Parmesan evenly over the croissants.
Bake for 12 to 15 minutes, or until the cheese is melted and bubbly and the croissants are golden brown.
Remove from the oven and garnish with chopped parsley and crushed red pepper flakes if desired.
Serve warm.