Mix well onion, lemon juice, olive oil, cilantro, salt and pepper in a medium bowl. Add crabmeat to half of the onion preparation and mix. Set aside.
Dice avocado in small cubes and mix gently with the rest of the onion preparation. Correct seasonings.
Place a ring over a plate and place inside a scoop of the avocado mix. Then place a scoop of the crabmeat mix over the avocado. Press lightly. Remove the ring.
Decorate, with lettuce if desired, or with the balsamic vinegar reduced with sugar over the stove for 5 to 10 minutes, approximately, until it reduces to half its size.
Other salads to taste:
Caesar´s salad with chicken
Light greek salad