I've never seen green tea mochi that needs to be prepared beforehand, but there is mochi that they sell in hard bricks that have to be toasted or boiled before you can eat them (well, I suppose you could eat them hard, but it wouldn't be very fun).
This is just the first Google result that popped up, but you can see a picture of the mochi in their little individual wrappers as well as what they look like on the grill.