Can indirect damage be designated to a zone that is already burning? I would assume no, but I couldn't find anything in the rules that said otherwise.

Had a game in which a follower's of Mork (deals 2 indirect damage when it comes into play), And the opposing Empire player, had a burning zone.

Weirdness - I just posted this question (as the 2nd of two rules questions) just now. Great minds think alike. My hunch is no but who knows what the true ruling will be.