Hmm... looking up recipes, Kiyoshi might have to resort to using what's left in Forest's spice cabinet as flavoring because Forest's supply of fruits and veggies was demolished (including her oranges and lemons... poor Fore, everything that was dear to her so suddenly taken away until now).
But yeah, if I remember right, it's a matter of finding good chicken stock, chopping the chicken into chunks, cooking up some sort of noodles or pasta, and mixing them all together. Kiyoshi could get creative with his spices possibly, like maybe a hint of curry powder to give it a kick for instance, or some ginger maybe, or maybe something more simple like paprika or rosemary? Honestly, I'm not an expert myself, though I could ask my mom later and see if she has any suggestions. Otherwise you could go along the lines of what I suggested and improvise.
Probably thinking of what type of noodles he wants to use would be a good start. Does he want thicker ones or angel hair, or even want to do something unconventional and put in bow ties or the curly cue ones or something similar?