Which ingredient adds a spicy element to the Italian sub?

The ingredient that adds a spicy element to the Italian sub is hot peppers. These peppers, which can vary from mild to very spicy, provide not only heat but also a lively flavor that complements the other ingredients commonly found in an Italian sub, such as meats and cheeses.

Hot peppers enhance the overall taste profile of the sandwich, creating a contrast with the saltiness of the meats and richness of the cheese. This makes them a popular choice for those looking to add an extra kick to their meal. While red onion can contribute some bite and mayo offers creaminess, neither of these ingredients carries the same heat that hot peppers do. Olive oil primarily adds richness and moisture rather than spiciness. Thus, hot peppers are essential for introducing that desired spicy element to the dish.