We have a really good Japanese place in the next town to us and they are the first place I had udon noodles. They are a bit big for me but I do see the appeal. I think the ones I like best are called soba. They don't put spinach in theirs but I can see it being very tasty. I haven't had Okinawa spinach before and it might not grow well here because of how cool it is but I will look into it because I remember watching a video on greens and heard it is one of the most nutritious.
I love soba noodles too! I haven't had them for ages as they are more expensive than the ready made udon I buy, but I love them! So good. It might grow in your greenhouse? Yeah it's meant to be really good for you, and it's just something different - variety is the spice of life isn't it?