Some later Aveos have a built-in "trip computer" in the cluster called the Driver Information Center (DIC). It shows info like average MPG (resettable), distance to empty, outside temp, etc.
(NB99Z's "unhidden" DIC, showing distance to empty screen)
If you have an '07 or newer sedan, or '09 or newer hatch with this style cluster, but showing only a smaller LCD odometer instead of this larger DIC, you can uncover the full, hidden screen and enable its features. The bigger LCD screen is already there - it's just mostly hidden behind your cluster's face/overlay:
The catch is: you have to add a switch to be able to change between screens. If you cut out/expand the "window" in your cluster's face/overlay to reveal the full LCD, you will only see the temperature screen by default. But you will have no way to change screens to see or reset your average MPG, distance to empty, etc.
To be able to change screens, you need to add a momentary switch to the cluster. To wire the switch, you'll need to be good at de-soldering & soldering, because you have to unsolder the LCD to separate the cluster assembly to access the spot where the switch has to be soldered to the circuit board.
But it can be done, and several members have done it already, posting photos & instructions.
Details are in this thread:
Thread: Add a DIC instrument cluster to a 2010 Aveo5 LS