In a mixing bowl combine ground beef, egg, mayo and taco seasoning. Mix until well combined.
Heat a grill pan to medium and spray lightly with cooking spray. Separate the meat into 8 thin patties.
In a separate small bowl, combine reduced fat cheese and salsa. Divide evenly on 4 of the patties. Top those patties with the other 4 and seal the sides.
Add beef patties to the pan (in batches if necessary) and cook on each side about 5 minutes or until no pink is showing. The temp of the beef should be 155F.
Slice up a tomato or other toppings as desired and serve with a vegetable side dish.