Preheat a large griddle to 375° or a large 12-inch skillet to medium-high heat.
In a large bowl combine the minced cube steak, ground chuck, 1 tablespoon of steak seasoning, a pinch of red pepper flakes and a quarter cup of steak sauce. Mix by hand until thoroughly combined
Divide into 4 portions, form into large patties and sprinkle with a little of the remaining steak seasoning.
Once the griddle is hot add in enough oil to coat the pan. Scatter the onions down onto the griddle and cook until slightly soften and golden brown. Remove and set off to the side.
Add a little more oil to coat the griddle and lay the patties seasoned-side-down. Make a divot in the center of each burger patties and season with more of the steak seasoning. Cook the patties for about 6-8 minutes before flipping, laying down the cheese and then cover with a dome lid to steam the cheese and get it all melted.
Remove the burgers to a clean plate and top with the griddled onions.
Separate the buns and place down on the griddle for 2-3 minutes to toast.
Serve the steak burgers on top of the toasted pretzel buns with a drizzle of more steak sauce.