In your Instant Pot, combine beef skirt steak, water, a large slice of onion, and sea salt. Set to high pressure and cook for 20 minutes, then allow for natural release for 5 minutes before releasing any remaining pressure.

Once the pressure has released, remove the skirt steak and shred it into bite-sized pieces using two forks. Set the shredded beef aside.

Chop the salad vegetables: shred iceberg lettuce, dice serrano chili, and tomatoes, finely chop the remaining onion.

In a large mixing bowl, combine the shredded beef with the prepared vegetables, seasoning with additional salt, black pepper, and olive oil. Squeeze lime juice over everything and toss together.

To serve, plate the salad with slices of avocado and sprinkle with cilantro.