Preheat oven to 350°F.

Spritz a medium baking dish with the olive oil spray.

Cut the tops off of the peppers and clean out the seeds; set aside.

In a bowl, mix the beef, onion, egg, and 1/2 cup of salsa.

Stuff the peppers with equal amounts of the meat mixture.

Arrange them in the baking dish, and top with the remaining salsa.

Bake, uncovered, for 1 hour until peppers are soft and meat is cooked.