This is a sort of battle plan I came up with walking home one day concerning the season finale. Since nobody in the show has bothered to take Zaheer seriously and plan accordingly I decided why not do it myself. Here goes nothing.
Zaheer knows Korra's coming, that's a given. He will undoubtedly assume she's not coming alone either and can easily surmise Asami, Mako, and Bolin will accompany her. Furthermore, if he knows Opal's training at the Northern Air Temple, and there's every reason he should, then it's not that much of a stretch to assume Su will tag along with a squad of metalbenders. It is important for Zaheer to know or guess the composition of Korra's party so he can act accordingly. This leaves a number of characters outside of Zaheer's purview, such as Lin, Tonraq, and even Varrick, enabling them to act covertly. More on that later.
A key point before his meeting with Korra is to ensure he has the upper hand regardless of the scenario. To that end, I imagine he'll come up with the following strategy. First, as we saw in the previous episode, P'Li will remain on an airship, ready to take down Korra's airship and only means of escape or take shots at Team Avatar on the ground. Second, Zaheer also needs to ensure the airbenders are at a safe distance from the rendezvous and he must assign someone to keep watch over them and, if necessary, execute them. I think the person best suited for this task would be Ghazan. All he needs to do is lock them up in some building that he'll be perfectly able to bring down with his earth bending or melt with his lava bending. This leaves Ming-Hua and Zaheer to attend the rendezvous what means it'll have to take place in an area close to a water source of some kind. Furthermore, it will have to be an open area for a number of reasons. The first and foremost is so P'Li can have a clear view of where everyone is at any given time should she be required to intervene. The second and perhaps less likely is so Korra's airship can land thereby restricting her ability to make a quick getaway.
A couple of pointers to help us determine the location where the airbenders are being held. First, if something goes wrong, Zaheer needs to contact Ghazan quickly in order to enact Order 66. The most likely scenario is that he'll use P'Li to that end, probably with her firing a shot at Ghazan's location as the dreaded signal. Second, should everything go okay, Ghazan will have to escort the airbenders to Korra's airship using a route within P'Li's line of sight. I think Team Avatar should be able to determine a relative location between these two.
What's the plan then? As I said before, Zaheer is expecting the following people to come off the airship: Korra, Asami, Mako, Bolin, Su, and a squad of metalbenders. That gives Lin, Tonraq, and Varrick, the element of surprise. Varrick will be crucial to the success of this plan. After his prison break at the end of Book Two he managed to perfect his flying backpack so that it now features a booster and a more advanced exoskeleton for the wings, increasing its range and autonomy. The idea will be for Lin to use this jetpack to approach the temple undetected from a different entry point and quickly make her way to the general location where the airbenders might be held. Once she's close enough she can use her sensory skill to pinpoint their exact location. There's a number of reasons why I'm sending Lin alone but it basically comes down to skills (earthbending) and experience, not to mention sending too many people would increase the chances of their being detected. I realize a lot's riding on Lin but she'll have to neutralize Ghazan (she'll have the element of surprise on her side) before Korra arrives. Once that's done she can fire a flare to indicate success but only after Tonraq radios her to do so.
This takes care of Ghazan but P'Li is no less of a threat. Well, the way I came up with getting rid of her also comes down to Varrick and perhaps Asami as well. I probably got the idea when someone mentioned P'Li's airship was flying itself. I figured it may have something similar to an autopilot but why not take it a bit further? What if (and it's a mighty big if) these airships have a system that allows for remote control? You would have to be close to remotely hijack the airship but it's nothing Varrick and Asami can't figure out. Once Korra's airship lands and everyone descends, Varrick can divert P'Li's airship forcing her to return to the cockpit to regain control of the vessel. It is at this time that Tonraq will radio Lin to fire the flare. If we want to make the diversion even more successful, we could have two or three metalbenders attack P'Li's airship using Varrick's jetpacks.
At this point, both Ghazan and P'Li will have been successfully separated from Zaheer and Ming-Hua. Undoubtedly, Zaheer will try to rescue P'Li but I don't think he can leave Ming-Hua to face off against Korra, Asami, Mako, Bolin, Su and a squad of metalbenders, on her own and expect her to triumph. After this, the result is pretty much forfeit. If Mako had any brains, he would use his lightning to electrocute Ming-Hua as soon as possible thus taking her out of the fight but that's a minor detail. And I highly doubt Zaheer can pull off the same trick he used on the Earth Queen on so many people in just a few seconds.
Et voilà! Team Avatar has just won a fight by outsmarting their opponents. A bit dull maybe but we can't deny it's both effective and efficient. 
PS: Needless to say, none of this will actually happen.