For the crab salad finely chop the crab meat into very small cubes.

Combine the crab with the mayonnaise, ketchup, pepper, salt and lemon

Chop the tomatoes into small cubes

Cut the onion and avocado into thin slices

As an additional step you can toast your bread with a little of unsalted butter

Assemble your sandwich, drizzle over some balsamic vinegar or apple cider vinegar