Chop the onions and potatoes into 1/4-inch pieces. Over medium heat, cook the onions in 1 tsp. oil for 1 minute.
Add the potatoes and cook for 10 to 12 minutes until the potatoes start to brown.
Add the chorizo and cook for 12 minutes until the chorizo has given up most of it fat.
Beat the eggs with 1/2 tsp. salt and pour them into the pan with the chorizo, potato, and onion. Let the eggs set for one minute. Then turn. Cook until the eggs have just set and break up the eggs with your spatula. Cook for couple minutes more until all of the egg has cooked through.
Meanwhile, cut the avocado into 1/4-inch pieces. Slice the spring onion into very thin rings including the 2-inch of the green stem.
Heat the tortillas in a dry pan until they start to puff up and become pliable. Don't overheat and let the tortilla become crispy which makes it difficult to roll.
On the warm tortillas, place the chorizo and eggs, then add about 1 oz. of crumbled cheese, a couple tbsp of diced avocado and 2 tbsp of salsa.
Fold the bottom of the tortilla up about 1-inch then fold the sides of the tortilla in about 1-inch. Roll the burrito tightly tucking the sides of the tortilla in as you go. It should form a tight cylinder with even ends.
Slice the burrito in half to serve.