Grease a 12-inch rectangular bread mold with a bit of oil.

Cut the causa carefully into six slices and place one slice on top of the lettuce on each serving plate.

Add more of the relish and a dollop of the reserved crab meat mix on top of each slice. Serve immediately.

Line it with 2 large pieces of plastic wrap, making sure they overlap so all the bottom and sides of the mold are covered and there is enough wrap on the sides of the mold with which to fold over and tightly cover the causa once it has been assembled. Set aside.

For the relish, put onions and vinegar into a medium bowl, cover and set aside for 45 minutes.

Meanwhile, place the jalapeños and their juice into a blender and blend until smooth.

Strain the mixture through a fine sieve, separating the juice from pulp left over.

Reserve juice and pulp separately in small bowls.

Strain the onions, discarding the vinegar and return to the bowl.

Add cilantro, salt and pepper, 1/2 cup of the yellow peppers, lime juice and 1 tablespoon of the reserved jalapeño pulp.

Cover and set relish aside. (Reserve remaining jalapeño pulp and juice for later use in the causa.)

For the causa, place potatoes in a large pot and cover by 2 inches with cold water.

Add 2 tablespoons salt and bring to a boil over medium-high heat.

Cook for about 25 minutes, until potatoes are tender when pierced with a knife.

Drain and let potatoes cool until you can handle them safely.

Peel potatoes and press them through a potato ricer or the fine side of a cheese grater, making sure no lumps remain.

Transfer potatoes to a large bowl and add the juice of 1 lime, oil and 1/4 cup of the reserved jalapeño juice.

Mix with a potato masher, adding 1/4 teaspoon salt and 1/4 teaspoon pepper. Place in the refrigerator until cooled.

Meanwhile, mix crab meat with mayonnaise and juice from 1/2 a lime.

Season with 1/4 teaspoon salt and 1/4 teaspoon pepper, cover and refrigerate.

Put avocados, remaining juice from 1/2 a lime, remaining 1/4 teaspoon salt and remaining 1/4 teaspoon pepper into a bowl and toss gently to combine.

Use a large spoon to spread one-third of the potato mixture into a layer at the bottom of the bread mold.

Arrange half of the avocado slices in the mold for the next layer, making sure all corners and sides of the mold are covered.

Transfer about 6 dollops of the crab meat mixture to a small bowl, cover and refrigerate for later use.

Spread half of the remaining crab meat mixture into the mold to make the next layer.

Press down firmly with the back of a spoon.

Repeat with one more layer each of the potato mixture, avocados and crab, then finish with a layer of potato mixture on top.

Fold the plastic wrap over the top of the mold to cover completely.

Press down slightly along the top of the mold, then refrigerate for at least 1 hour.

To serve, carefully uncover the plastic wrap and unmold the causa over a serving plate.

Spread some of the reserved relish over the top of the causa.

Arrange lettuce leaves on 6 serving plates.