Chazuke is not porridge because it's not cooked. It's a simple and clever way to serve left-over rice invented before microwave ovens were avaiable. Just pour hot tea over left-over cold rice, no flavoring necessary but you could add an umeboshi or iriko (tiny fish). Nowadays, there are all kinds of furikake flavoring. I think wasabi is the least popular, salmon and nori are more common.
Here's an article on it for a "recipe," if you need it.
Ochazuke (green tea over rice) recipe - Bento.com
But I think using hot rice for chazuke is a waste. You could eat the rice with the added flavoring without adding ocha.