In a medium bowl, mash the avocados with a fork until nearly smooth. Stir in the garlic, onion, 2 tbsp. cilantro, the lime juice and 1/2 tsp. salt. Cover with plastic wrap touching the surface and let sit for about 2 hours to allow the flavors to develop.
Discard the plastic wrap and season the guacamole to taste with salt. (Remember: The tortilla chips are salty.) Transfer the mixture to a serving bowl, garnish with cilantro and serve.