All the food that we eat is broken down into 23 amino acids, our bodies produce 15 of these naturally but the remaining are the 8 essential amino acids which have to be eaten in foods or taken in supplements.
Quinoa contains all 8 of the essential amino acids, so it is a complete protein. It is not a grain it is the goose foot plant's seeds. It is gf and is a pseudo grain so it is not even a distant relative of wheat so unless you have an intolerance to it, it has many health giving properties, please see the links. It is available in health food shops. Just check the packet about washing instructions as the grain usually needs washing to remove a white chalky coating then boil as per instruction.
You can also buy quinoa flour and add that to other gf flours for baking and sauces. Well worth checking out for coeliac, methinks. The Inca's called it the 'mother grain' and considered it a super food.