Olive oil adds wonderful flavor to giardiniera, but note that extra virgin olive oil will solidify in the refrigerator, unlike refined olive oil. The same goes for avocado oil. I use avocado oil and extra virgin olive oil because they're what I always have on hand. If you'd like to do the same, just plan to take your pickled vegetables out of the refrigerator for 15 minutes or so before you plan to enjoy them to give the oil time to warm and liquify. Otherwise, use a vegetable oil like canola oil and refined olive oil that won't solidify when cold.