This is an insanely simple quest, though a little tricky to get the Poison Lizard to spit where you want them too. The best course of action is to sacrifice a bit of HP to get what you want. A good way to get them where you need them is by getting them to notice you and pursue you around the chop points. If you get a little distance between you and them (at least one space) and move around from side to side (around the gather point of course) for instance they'll likely spit up their toxic goo on to the point so you can collect the Cork Bark. Though sometimes you end up battling them as well so make sure you're prepared to do battle! A group of at least 30-35 should be able to handle them with ease!