Heat the ground beef and onion in a skillet over medium high heat on the stove. Cook until the meat is completely browned and the onions have softened. 

Drain any excess fat from the skillet. 

Sprinkle in the taco seasoning and stir the meat to combine. 

Cut the avocados in half lengthwise and remove the pit. 

Scoop out the flesh from the inside of the avocados. 

Fill the avocado shells with the taco meat and top with shredded cheese, sour cream and salsa. 

Add green onions for garnish before serving.