Boil water in a large pot and cook udon noodles for 8-10 minutes until tender.
Drain the noodles and set them aside.
In a separate pot, heat the dashi broth over medium heat.
Add soy sauce and mirin to the broth for flavor.
Introduce the sliced shiitake mushrooms and cook for 5 minutes.
Add the chopped bok choy to the broth and simmer for 3 minutes.
Gently add the cubed tofu to the pot, allowing it to warm through.
In a bowl, place a portion of udon noodles.
Pour the hot broth with vegetables over the noodles.
Garnish with chopped green onions and a drizzle of sesame oil before serving.