Heat a stove-top griddle with cooking spray and set over medium-high heat to preheat. Place red onion slices on hot pan and sear 2 minutes per side, flipping with a spatula, until golden brown and slightly softened.
Arrange steak slices alongside onion. Cook 2 to 3 minutes, until hot. Place cheese on top of steak and cook 1 minute, until cheese melts.
In a small bowl, whisk together mayonnaise, honey and garlic flakes. Season, to taste, with salt and freshly ground black pepper. Spread mayonnaise mixture on rolls and top with seared onion slices and cheese-smothered steak.