They'll meet like this:
Everyone is moping around, feeling confined in the city.
Katara: C'mon, I heard of this fantastic tea shop. Let's go check it out.
Sokka: How would tea help us at all?
Aang: Well, tea is supposed to calm the mind. Maybe it'll help us think of a way to find Appa.
Toph: And tell everyone of the war, and get the Earth Kingdom military to help us.
Aang: Yeah, that too.
So they go to the tea shop where Iroh and Zuko are working and take a seat at a table.
Sokka: Oh waiter! Get over here, the Avatar has arrived.
Owner: The Avatar? Quick, cater to his every whim!
Iroh and Zuko exchange a glance.
Zuko: *thinking* Must...resist...obsessive compulse...to capture... *Goes to serve*
Aang: Okay, I'd like... OMG! Zuko! *He, Sokka, and Katara all get into a fighting stance. Toph raises an eyebrow*
Katara: How'd you find out where we were going?
Sokka: And how'd you manage to get into the Earth Kingdom capital?
The other customers are all staring.
Zuko: *through gritted teeth* What-would-you-like-to-order?
Now the Gaang is staring.
Zuko: *hushed tones* I'd like to keep my job, thank you very much.
More stares.
Zuko: What?
Katara: You...work here?
Sokka: As...a waiter?
Aang: At a..teashop?
Zuko: Look, I didn't pick the place, my uncle did.
Toph: So Gramps is okay?
The stares are directed at Toph now.
Toph: What?