Halve, seed and scoop the avocados out of their peels and place in a large bowl. Add the juice from the lime and toss to coat the avocado completely. Drain, and reserve the lime juice for later use.
Add the salt, cumin, and cayenne pepper to the avocado bowl and mash using a potato masher. Then fold in the onions, jalapeno, tomatoes, cilantro, and garlic. Add 1 tablespoon of the reserved lime juice.
Let it sit at room temperature for 1 hour, then serve.