Yes quinoa is kosher for Pesach, but needs supervision. It is not kiyniyos. Even the OU has accepted it. As to the entire kitniyos issue – I am Ashkenaz and therefore do not eat Kitniyos, but I am frustrated at the chumrah that the Ashkenazic Rabbanim added to what is already assur as chametz. Hashem didn’t say, “If it resembles chametz, it’s assur on Pesach,” (if so, all the Pesachdig crepes and lukshen would be assur). He said there are five grains that could become chametz and they are assur. Why did our chachomim add to the burden by assering certain yellow and green vegetables, not to mention rice, which does not even grow in the ground, just because those vegetables can be ground up to resemble flour? So can potatoes for that matter, be made into flour (actually, the rabbanim WANTED to asser potatoes, but they would have had a major rebellion on their hands, as it was such a cheap staple of all Jewish homes).
I follow the halacha and minhag Ashkenazim, but I have never understood the rationale for this issur. To say something grows near a potential source of chametz – that I can understand. But if the item is kept totally clear of wheat fields, etc., what’s the difference if it looks like a grain before it’s cooked? It’s NOT one of the five assur grains!!!!! And quinoa is a great source of excellent protein, too.
BTW, off-topic, does anyone have good kugel or cake recipes for Pesach that are not made with nuts or eggs? I am going crazy trying to make a starchy side dish besides farfel.