Chopped Cheese

Preheat a large flattop griddle to medium, or heat a large cast-iron griddle on the grill or cooktop over medium-high. Cut rolls horizontally, leaving 1 side attached as a hinge. Toast, cut sides down, on griddle until lightly browned, 1 to 2 minutes. Remove from griddle.

Drizzle oil evenly over griddle; top with ground beef. Using a large metal spatula, flatten into an even layer, about 1/2-inch thick. Sprinkle with sazón, and top with onion and jalapeño (if using). Cook, undisturbed, until beef forms a golden brown crust on bottom, 4 to 6 minutes. Chop and stir beef mixture using spatula; cook, chopping into small crumbles, until beef is cooked through and crispy in spots and onion is softened, about 4 minutes.

Shape beef mixture into a 14-x 5-inch rectangle on griddle using spatula or a metal bench scraper. Top beef mixture evenly with cheese slices. Let stand, undisturbed, until cheese melts, about 1 minute.

Spread each toasted roll with 2 tablespoons mayonnaise and 1 tablespoon ketchup. Transfer about one-quarter of beef mixture (about 1 cup) onto each roll; top with tomato slices. Season tomato slices with salt and pepper to taste; top each with shredded lettuce. Wrap each sandwich tightly in parchment paper or aluminum foil; let steam for about 5 minutes before cutting sandwiches in half. Serve hot.