Yes, you may definitely make this well ahead but do not add any oil, garlic, or onion until ready to eat. These will oxidate and will make the dish taste rancid and stale. If planning to grill the eggplants ahead of time, do so, take these out from the skin, and allow them to rest on a reclined chopping board so that all juices drain out nicely. You may then place these with a generous sprinkle of salt in an airtight container and place them in the fridge for 3-4 days or in the freezer for up to a month. The dip can then be prepared in no time if stored in the fridge or thaw overnight in the refrigerator if frozen and use the next day. Just add the remaining ingredients, give a quick whizz, and ta-da!