A Japanese tomato noodle soup has many of the classic ingredients of Japanese noodle soups - a dashi broth, fresh udon noodles, soy sauce, ginger, garlic, mushrooms and bok choy. But it's the base of tomatoes and a dashi broth together that makes it truly unique.
Skin and de-seed tomatoes and roughly chop. Add 1 TBSP of oil to a sauce pan over medium heat, add tomatoes and simmer for 12-15 minutes, stirring on occasion. It should form a thick, soupy consistency.
While tomatoes are simmering, prepare garlic, ginger, onion and mushrooms. Add 2 TBSPs sesame oil to a stock pot over medium heat and add everything except garlic. Saute for 5 minutes and add garlic in the last minute, stirring frequently.
Add 2 TBSPs soy sauce and taste. Add more, if desired, to taste.
Prepare fish however you'd like - pan fry in sesame oil, broil, bake or grill. You can start this step (and the next one) while soup is simmering.
Prepare udon noodles according to package directions. If using fresh udon noodles, place in boiling water, turn down heat and gently simmer for one minute. Immediately remove from heat, strain and submerge in cold water to keep them noodles from cooking further. Mix with 1 TBSP toasted sesame oil.