During the celebration of Passover, it's traditional for participants to avoid all types of leavening, like yeast. In fact, you could say this is one of the most important, key features of the entire celebration.
probably not celebrating the Seder. And, at least to my knowledge, there are no Buddhist Seders or New Age Seders or Ed Hardy Seders; Jews pretty much have a corner on the Seder market.
(Although, all things being equal, maybe I should write it on a chocolate bar.)
Update from john: [rubbing temples] To those of you currently chilling in the Epcot Bunker™, yes, anyone can make a lovely Seder. Apparently there are [insert comment count here] non-Jews doing so.
It's still Jewish.
That is all.