Using a sharp knife, slice the avocados in half, circling the pit. Open and on the pit half, either remove using a spoon or wedge knife blade into the pit and twist to remove. Scoop the flesh from the skin and place in medium bowl. Discard pit and skins.
Slice lime or lemon (my preference) and squeeze a half (at least 2 tablespoons) over avocados and gently mash. Season to taste with salt and more citrus juice to desired taste. Set aside.
Dice the onion into small 1/8 to 1/4 inch pieces. Rinse under water in strainer and shake excess off. Transfer to mashed avocado bowl and add the tomato, chilis and cilantro.
Gently fold everything together, season to taste again and serve chilled or at room temperature with tortilla chips or as a condiment with tacos or grilled meats.