Squeeze half a lime into a bowl. Add the oil and cilantro and mix well.
Add the lime zest, mango, bell pepper, onion and jalapeno and mix well.
Add the crab and mix gently.
Drizzle the remaining lime juice over the avocado.
Place 1/4th of the avocado in the bottom of a large round cookie cutter or metal ring. Tamp down slightly with the bottom of a spoon.
Add in 1/4th of the crab salad and tamp down. Slowly remove the cookie cutter. I put a spoon on top of the salad mixture to hold it down while removing the cookie cutter.