Wash the chopped red onion with cold water to eliminate the intense flavor, drain well.
In a large bowl place the avocados, begin to crush them a little until you get to have a purée, can be done very easily with a fork. If you plan to use emental cheese for your guacamole, you must add it now.
Add chopped tomato, garlic, cilantro, onion, and lemon juice. Continue crushing the avocado until the ingredients are combined and the pure has the desired consistency.
Add a little cayenne pepper, and a little salt, mix for several minutes.
Serve with nachos or as an accompaniment to Mexican dishes.