Preheat oven to 350 degrees F (175 degrees C). Lightly grease a medium baking dish.
In a bowl, mix the cooked rice, beef, onion, egg, salt, and 1/2 cup salsa. Stuff orange, yellow, and red bell pepper halves with equal amounts of the rice mixture. Arrange pepper halves in the baking dish, and top with remaining salsa.
Bake uncovered 1 hour in the preheated oven, until peppers are soft and filling has reached a minimum temperature of 160 degrees F (72 degrees C).