Add the ground beef, Worcestershire sauce, and garlic powder to a bowl and work it together with your hands to distribute the seasoning throughout the meat, being careful not to overwork the meat.
Portion the meat into 8 loosely packed balls, 2 ounces each.
Heat a large cast iron skillet or flat top grill over high heat. You want this to be very, very hot before cooking the burgers.
While the skillet or grill is heating, slice the pepper and onion into very thin slices.
If you’re working in a skillet you’ll want to make two burgers at a time. If you’re working on a larger surface, you can make all of the burgers at once. Add a small amount of butter in each spot where you will place a burger patty and then drop a few slices of onion and jalapeno into a little pile over the butter. Let cook for 1-2 minutes to brown a bit.
Add the balls of beef to the skillet or grill directly on top of the piles of onion and peppers. Immediately smash each one with a burger press or two large spatulas. The burgers should be smashed very thin, a bit larger in diameter than your hamburger buns as they will shrink a bit as they cook.
Sprinkle the flattened burgers with salt and pepper.
Let the burgers cook until the edges are browned and the tops are turning more of a gray-ish color, 45-60 seconds.
Flip the burgers, season again with salt and pepper.
Immediately drop spoonfuls of pimento cheese on top of each burger, working quickly. If you’re cooking on a flat top grill, you should be able to cook all the burgers at once, working quickly so as not to overcook the burgers.
Immediately stack 4 of the burgers on top of the other 4 burgers, making 4 double patties.
Remove from the grill and place the burgers on the toasted buns and top with thin slices of tomato and shredded lettuce. Serve immediately.