Preheat Blackstone griddle to medium-high heat. Drizzle vegetable oil then add the onions and jalapenos. Sauté for 5-7 minutes until tender and lightly charred. Lightly season with salt and pepper.
Place the 4 ground beef portions onto the griddle. Smash thin with a burger press or large hamburger spatula. Season with salt and pepper. Lay the pastrami to the side and cook for 2 minutes per side until crispy.
Flip the burgers, and top with crispy pastrami, peppers, onions, and Swiss cheese. Cover for 2 minutes until fully melted. Toast the buns off to the side while the cheese is melting.
Remove the buns from the griddle, and lather each side with thousand island dressing. Place the burgers onto the buns and serve immediately.
