In a medium bowl, mash together the avocados, lime juice, and salt.

Mix in onion and garlic.

Stir in cayenne pepper. (optional)

Place the avocado seeds in the bowl to help prevent the avocado from discoloring.

Serve immediately, or cover with plastic wrap and refrigerate 1 hour for best flavor. Make sure that the plastic wrap is touching the avocado directly to avoid discoloration.