Definitely. If you have a small griddle or cast iron skillet, cook the onions first over medium-low heat, until soft and caramelized, then transfer them to a bowl and keep warm. Increase the heat to medium-high and add the burgers, smashing them to create a thin patty. Cook, flipping once, until golden and cooked through. Add the cheese and let it melt. Transfer the burgers to a plate. Toast the buns on the hot griddle or skillet, if desired, then assemble your burgers with spicy mayo, burger patties, and caramelized onions.