In a large bowl, place all but 1/4 cup of the avocado pieces. Add 2 tablespoons of the lime juice, 2 tablespoons of the cilantro, 1 teaspoon of the jalapeno, 1/2 teaspoon of the cumin, 1/4 teaspoon of the garlic, 1/4 teaspoon of the salt, and a pinch of cayenne, and mash with the back of a fork until smooth. Add 1/4 cup of the onions, 1/4 cup of the tomatoes and 1/4 cup of the jicama to the avocado mixture, and stir well to combine. In a separate bowl, combine the remaining ingredients with the crabmeat and gently toss to combine. Fold the crabmeat mixture into the mashed avocado mixture, stirring to combine, but being careful not to break up the crabmeat.