In a bowl, combine tuna, mayonnaise, Dijon mustard, chopped Calabrian chili peppers, giardiniera, garlic, grated onion, celery, and celery seed.Season with salt and pepper and mix until creamy and evenly combined.Taste and adjust seasoning.
Butter the sourdough bread and toast it in a skillet over medium heat until golden.
Sprinkle shredded pepper jack directly onto the toasted bread.
Top the cheese layer with tuna salad.Add another layer of pepper jack cheese.
Cook the sandwich in the skillet until the cheese melts and the bread becomes deeply golden.Finish with a drizzle of spicy hot honey just before serving.Sprinkle crushed Cheez-It crackers over the tuna mixture for salty crunch.