Heat 1 tbsp oil in skillet over med; thinly slice onion + sauté 8-10 min until browned; season with salt + add 2 tbsp water; cover + cook 3-5 min until softened

Heat lightly oiled skillet over medium; cook burgers 10 min, flipping every 1-2 min to avoid burning until hot + fully cooked; remove pan from heat, top burgers with 1 slice of cheese + cover until cheese melts, about 1 min

Toast 2 buns until warm + golden; spread 1-2 tbsp sauce onto each bun

Divide cheese burgers + caramelized onions between buns—perfection.