Blinding Flash stands a good chance of doing good damage to a zone of zombies cheaply due to the +2 vs non living. Even if it doesnt it stands a great chance of daze/stunning them for the same reason.
Temple of Light is good against them too, even with no other temples on the table its an action-less, long ranged 3 dice of damage with a decent daze/stun chance. Supporting it and yourself with a Hand of Bim Shalla should be an obvious piece as well.
Stranglevine, Force Crush, Demonhide Armor and Corrode are sources of direct damage that can help.
Quicksand can usually mess with zombies too... since they have Bloodthirsty +0 they HAVE to try to attack a wounded creature in the zone, which means they cannot choose to attempt the escape roll and will eventually drown.