Prepare the sauce by mixing mushroom powder, togarashi, soy sauce, and mirin. Mix well until the powder has fully dissolved.
Cook the udon noodles according to package instructions. Drain then set aside.
Mix together salt and ground white pepper. Then, season the seafood on both sides.
In a pan, heat 1 tablespoon of oil over medium-high heat. Sear the shrimp and scallops for 2 minutes on each side. Remove and set aside.
In the same pan, heat 1 tablespoon of oil over medium-high heat. Cook the squid for about 1 minute then remove and set aside.
Heat the remaining tablespoon of oil in the same pan. Add onions and garlic, and cook for 1 minute until fragrant.
Toss in the carrot and cabbage, and cook for about 2 minutes until tender.
Add the udon noodles, seafood, and sauce. Mix until the noodles and seafood are well coated.
Garnish with chopped scallions, togarashi, and bonito flakes. Serve and enjoy!