Combine 1 tablespoon of the chopped onions, ½ teaspoon of the chopped jalapeno and ½ teaspoon of the cilantro with ½ teaspoon of salt in a bowl.
With the back of a wooden spoon mash these ingredients into a paste. This releases the juices within.
Split the avocado in half, then remove the seed. Slice the avocado lengthwise in about 1/8-1/4 inch strips, and then across, forming a grid. Scoop the avocado out of the skin with a spoon (never mash or scrape it).
Add the avocado to the paste and fold to combine thoroughly. Add the other ingredients, folding gently, taking care not to mash the guacamole.