Which ingredient is NOT used in the patty melt?

The patty melt is a classic sandwich known for its combination of flavors and textures, typically featuring a hamburger patty, cheese, and grilled onions, all grilled between slices of bread. In this case, the correct answer identifies romaine lettuce as the ingredient that is not used in a traditional patty melt.

This sandwich focuses on savory ingredients like grilled onions to add sweetness and depth, along with the hearty texture of Texas toast for a satisfying crunch. Peppers, while they can bring additional flavor to many dishes, are not a standard component in the classic preparation of a patty melt. Therefore, romaine lettuce, being a fresh and crisp salad green, does not fit into the typical flavor profile or texture of this sandwich, making it the ingredient that is not included in a patty melt.