Place garlic and salt into a bowl that’s a little larger than you think you need. Using a fork, smash and grind the salt and garlic against the bowl until almost smooth. It can be left a bit coarser if you want a stronger garlic flavor.
Cut the cilantro stems in half, discarding the bottom half of the stalks. (I like to include the remaining stems because I feel they add a nice variation in texture.) Mince the leaves and their attached stems to a fairly even size. Set aside.
Place avocado chunks in the bowl. Immediately squeeze 2 of the lime halves into the bowl and toss to coat, largely to reduce browning. Then stir cilantro, onions, tomatoes and jalapeños into the avocado gently, trying not to break down the avocado too much.
Once all items are stirred in, adjust with remaining lime, salt and pepper to taste. Superstitiously place the avocado pits into the completed guac to help with decolorization — and also because it’s pretty.