Combine ground beef and chorizo in a bowl and divide meat into 4 patties.

Heat tablespoon of oil in a large frying pan over medium heat. Place patties in the pan and let cook, undisturbed for 5 minutes or until well browned on one side. Flip and cook another 5 minutes on the other side or until cooked through. Remove from heat and let rest in the pan while you make the onions.

Meanwhile, scoop avocado flesh into a bowl, remove pit and sprinkle with salt. Mash a few times with a fork to break up but not until smooth. Toast burger buns.

Heat oil in a large, heavy frying pan over medium-high heat. Toss onions with flour and salt until well coated.

Test to see if oil is ready by dipping an onion into the oil, it should bubble vigorously, if not, give the oil another minute or two. When oil is hot, Remove a handful of onions from the flour mixture and shake off excess flour. Carefully place in the oil and repeat until the pan is full but not crowded.

Let cook, undisturbed until browned on the bottom. Flip with tongs and cook the other side, about 3 minutes more. Remove to a paper towel-lined plate and sprinkle with salt. Repeat with remaining onions.

Spoon some avocado on the one side of the burger bun. Top with a chorizo burger, then some onions. Spread some mayonnaise on the top bun if you'd like and serve.