Prepare some herbed mayo by combining your mayonnaise of choice with fresh chopped rosemary and thyme, to taste.
Separate beef into 4 equal portions. Use hands to lightly form into patties the size of your buns. Once you have formed the patties, season generously with a blend of salt and pepper on both sides.
Take your oil and apply it to your skillet or flat top, grill onions until caramelized, and then remove.
Now that you have a hot cooking surface, add the patties and cook for 3 minutes until you get a good sear. Make sure to smash the patty until it's just about paper thin. This will create a sear and trap in any juices. After 3 minutes, gently flip the patties and then cover with the pepper Jack cheese. While you wait, lightly toast your buns.
To serve: Spread base of buns with the herbed mayo sauce/condiment of choice. Top with grilled onions and then hamburger patty. Pile over onions, then add more sauce/condiments. Top with lettuce and a lid of bun. Serve immediately.