In a medium bowl, mix to combine the mayonnaise, lime juice, tomato, cilantro, jalapeno, cayenne, and salt.
Drain any excess water from the crab meat, then gently fold it into the dressing. Be careful not to overmix, or you may break up the lumps in the crab.
Cut the avocados in half, and remove the pits. Season the avocado halves with salt and pepper.
Divide the crab salad between the four avocado halves, and serve promptly. Enjoy!
*I like 2 tbsp of jalapeno, but between that and the cayenne, this makes it fairly spicy. You can reduce the amounts if you want it to be milder.**Salt should be done to taste, depending on if there's salt added to the crab you're using.