Butter and toast the Brioche buns until golden brown.
Make the sweet and spicy pepper sauce.
Make the smash burgers by pressing balls of ground beef into a hot skillet with a sturdy spatula. Add onions to top, then flip.
Add cheese to smash burger and cook for 2 minutes more.
Assemble burger by adding it to the bottom half of the bun. Top with grilled onions, bacon, sweet and spicy pepper sauce, and top of bun.