To make the caramelized onions and peppers: Heat the oil and butter in a large skillet over medium-high heat. Add the onions, peppers, pinch of salt and pepper. Cook, stirring every few minutes, until onions are caramelized and peppers are tender and slightly browned, about 15 - 20 minutes. Remove from heat and top burgers.
Heat grill or large pan to medium/high heat. Gently coat both sides of the frozen burgers with oil. Place burgers on hot pan. Cook for 5-6 minutes on each side. Be sure the burgers are cooked thoroughly before removing from heat.
To assemble:
Place 1 leaf of Romain lettuce on each bun, drizzle desired amount of ketchup, top with burger and caramelized onions and peppers. Enjoy!