1. Heat a gas or charcoal grill & oil the grate lightly. 2. Split each avocado skin with a sharp knife, just piercing the skin. Peel the skin away, leaving the avocado whole. Cut the avocado in half lengthwise & remove & discard the pit. Lightly brush each avocado half with olive oil. 3. Arrange the avocado halves on the grill & cover them. Grill for about 5 minutes, then flip. Cover & grill for another few minutes, or until the avocados are heated through & have grill marks. (Keep an eye on them; I recommend doing them on a low heat; depending on your grill it could take less -- or more! -- time.) 4. Take the avocados off the grill & let them cool slightly. Smash them with a fork & stir in the juice from half a lime, along with some salt & pepper to taste. Add the garlic, onion & cilantro, if you wish. Serve immediately with chips.