Am I so predictable?
The other answers covered the translation part. I am going to give my two cents on the culture side.


  Is there a set-phrase that is often used to express this idea?


I don't think so, because traditionally Chinese don't really respond that way. If someone is 'predicting' your order, he's really saying 'I know what you like' as a gesture of intimacy, friendliness or at least, care. A positive response is usually along the line with 'exactly', 'you really know me', 'it's a pleasant surprise that you remembered', etc. I am not quite sure what subtext does 'am I so predictable' convey in English speaking culture, but a verbatim translation in Chinese doesn't sound very positive when used as a response to that 'predicting' conversation. Considering how uniformity, agreement and tacit understanding were valued in traditional Chinese culture, 'am I so predictable' might sound fun or sexy to some listeners, but it might be perceived as rejection, a perverse personality or a bad mood to some other listeners, depending on their social role and culture belief. I am not saying you shouldn't respond that way, just a reminder of how it could be received differently from your intention.

Some simple, low-key positive acknowledgements:


没错 (exactly)
你猜对了 (your guess is right)
你都记住了 (you remembered!)