Prepare all of the ingredients.
In a large sauce pan over medium-high heat, add oil, onions and garlic. Cook for 3 minutes then add ground beef, red pepper flakes, salt, mushrooms, and jalapenos. Cook until no longer pink.
Preheat griddle or grill pan to medium-high heat.
Combine sauce ingredients in a bowl.
Build the sandwich - start with slice of bread spread with sauce, add a slice of cheese, portion of meat mixture, slice of cheese, and slice of bread. (See photo in post)
Cook on griddle for 5 minutes on each side. Slice on the diagonal and serve up.