Chilled with tempura toppings
Hanamarudon is a franchise chain of Sanuki udon (originated from Kagawa prefecture in Shikoku) which is my favorite spot to go to . This might sound strange but I like my udon chilled topped with tempuras (Japanese fritters of vegetable, seafood etc).
Here is the menu online.
The one I like is the Ontama bukkake udon (hiya = cold/chilled) that has chilled udon with cold thick soy sauce mixed with bonito broth topped with some spring onion and a half boiled egg. On the side, I would get some tempuras as well. Check out the picture below of my recent meals there.
Cheap, good and quick.
For me, the best fast food ever in Japan. :)