Halve the avocados and remove the pits. Make two long cuts in the flesh of each half, and 5 or 6 crosswise cuts. Rub the cut surfaces gently with the smashed garlic. Squeeze the juice from the 1/4 lime evenly over the cut surfaces.
Place the remaining 2 tablespoons of lime juice, the cilantro, the jalapeno and the onion in the work bowl of a food processor. Puree.
Turn the cut chunks of avocado out of their skins and into a large bowl. Toss very gently with the cilantro puree and with the chopped tomatillo. Serve with tomatillo puree. Or, season well with salt and pepper, and serve immediately, garnished with cilantro leaves.
For the Tomatillo puree: Place all ingredients in the work bowl of a food processor. Puree. season well with salt and pepper.
When ready to serve, season the guacamole well with salt and pepper. Divide it among four wide, shallow soup bowls, placing a scoop of guacamole at the center of each. Spoon the tomatillo puree around the guacamole. Garnish the puree with cilantro leaves, and the top of the guacamole with a little finely chopped red tomato. Serve with warmed tortilla chips.