Preheat the Blackstone griddle to medium heat. Add oil, then cook the onions and mushrooms for 3-4 minutes, seasoning with salt and pepper. Push them aside to keep warm.
Place the ground ribeye balls on the hot griddle. Use a burger smasher and parchment paper to smash the burgers flat. Season with Blackstone Cheesesteak Seasoning. Cook for about 1.5 minutes, then flip. Top each patty with Cooper Sharp American cheese and let cook for another 1-2 minutes, until the cheese melts and the burgers reach your desired doneness. Add the cooked onions and mushrooms on top.
If desired, toast the slider buns on the griddle. Assemble the sliders by placing the patties on the buns. Add Sriracha ketchup and deli pickles if using. Serve and enjoy!
