In a bowl, use your hands to loosely mix the crabmeat, lime zest and juice, celery, red onion, and salt. Work gently so the crab doesn’t get stringy. Taste and add salt if desired.
To assemble, lightly oil a springform pan and line bottom with wax paper.
Neatly spread half the potatoes on the bottom, top evenly with the crab mixture, and finish with the remaining potatoes.
Release the sides of the pan, transfer causa to a large plate, and garnish with avocado, dots of aji paste, and piped mayonnaise.
To make individual servings, use small ring molds and tamp the layers down with the bottom of a glass. Serve cold.