In a large pot, combine chicken broth, water, miso paste, soy sauce, sesame oil, ginger, and garlic. Bring to a simmer over medium heat, stirring until the miso paste is fully dissolved. Reduce heat to low and keep warm.

In a separate pot, bring water to a boil and cook ramen noodles according to package instructions. Drain and set aside.

Set up a breading station for the chicken katsu: Place flour in one shallow dish, beaten egg in another, and panko breadcrumbs in a third.

Dredge each piece of cooked chicken in flour, then dip in the egg, and finally coat with panko breadcrumbs.

In a large skillet, heat about 1/4 inch of vegetable oil over medium-high heat. Once hot, add the breaded chicken and fry until golden brown and crispy, about 3-4 minutes per side. Remove and drain on paper towels.

To serve, divide the cooked ramen noodles among bowls, ladle the miso broth over the noodles, and top with sliced chicken katsu, green onions, and a soft-boiled egg if desired. Add nori sheets for garnish.