Preheat the oven to 350 degrees F. Line a baking sheet with parchment paper. Place the hot dog buns side by side on the baking sheet.
In a small bowl, beat the egg. Brush the top sides of the buns and sides with the egg wash and sprinkle on the poppy seeds. Transfer to the oven to bake for 5 minutes. Remove and set aside.
For the Hot Dogs
Bring a medium pot filled with water to a boil. Drop the hot dogs into the water. Boil for 3 - 5 minutes. Remove from the water.
Place the hot dogs inside each of the hot dog buns. Top each hot dog with yellow mustard. Then, add a handful of diced onion, a spoonful of sweet relish, two sport peppers, tomatoes and a dill pickle. Season top with celery salt. Serve.