I'm going to try out HIIT instead of LISS for a while, and I was wondering where to put my one carb meal for days I do cardio.

On my cardio days I usually stick to only one meal with carbs (and protein). Should that come right before HIIT, right after, first or second meal of the day...where?

With only one meal I would put it after for the insulin spike. A single carb meal prior to workout will do nothing for your glycogen.