Buckwheat noodles aka soba is actually wildly used in asian cultures. Many of their dishes using those noodles do include bean based products, and/or nuts, seeds. Pure buckwheat is a rather acquired taste and since you never ate it I'll assume you come from a place that doesn't locally use it so it's normal to not be aware of general taste/texture pairings. But grain like on OPs picture really doesn't play well with what you propose even if it might make sense strictly nutrition wise. Thankfully, human ingenuity helps to make food tasty as well as nutritious.