Preheat the Pan: Start by heating a cast-iron skillet or griddle over medium-high heat. You want it hot enough to sear the patties but not so hot that you burn the onions.
Prep the Onions: In a bit of olive oil, sauté the thinly sliced onions until they're caramelized – about 5-7 minutes. Set aside when done.
Shape the Patties: While the onions are cooking, divide the ground beef into large balls (about 4-6 ounces each).
Smash it Down: Once the pan is hot, place the beef balls onto the skillet. Using a spatula, press them down firmly to create a thin patty. Season with salt and pepper. Cook for about 2-3 minutes on one side.
Add Jalapeños and Cheese: Flip the burgers, immediately topping each with diced jalapeños and a slice of cheese. Cook for another 2-3 minutes, allowing the cheese to melt.
Toast the Buns: While the burgers are finishing, toast your burger buns in the hot skillet for just a minute or two until they're golden brown.
Assemble: On each bottom bun, layer a leaf of lettuce, followed by the cheesy burger, a generous scoop of caramelized onions, and tomato slices. Top with the other half of the bun.
Serve and Enjoy: Serve hot with your favorite sides, and dig in!
