Heat a flat griddle to medium-high.
Put the bun on the griddle to toast it. Then place the hamburger patty on the griddle and sprinkle with seasoning salt. When the bun is toasted, remove it from the griddle and set it in your prep area. Put the ketchup on the bottom part of the bun, then the pickles. Make sure to spread them out so that every flavor is in every bite.
Place the pastrami on the griddle and sear away. Flip the hamburger patty, sprinkle with seasoning salt and cook to desired doneness. Place the Swiss cheese on top and melt. Add the pastrami on top of the cheese. Top the pastrami with the grilled onions.
Now all you have left is the top part of the bun and the brown mustard. Squirt or spread the brown mustard on the bun top and place it on the grilled onions. Transfer the hamburger patty and toppings to the bottom part of the bun. Enjoy.
This recipe was provided by a chef, restaurant or culinary professional. It has not been tested for home use.