Cook the katsu chicken in the oven or air fryer as per packet instructions.
In a large pot over low heat, add a splash of oil and gently sauté the spring onions, garlic and ginger until very soft and translucent, about 5 minutes. Add the stock, then stir through the miso paste, soy sauce & sesame oil and bring to the boil. Leave to simmer for 5 minutes.
Add the noodles to the broth and let cook for a couple of minutes.
Place the noodles in two soup bowls and ladle over the broth.
When the chicken is ready, slice it into strips across the grain and place on top of the noodles. Drizzle the chicken with the katsu sauce and a sprinkle of sesame seeds and fresh sliced spring onion. Finish each ramen bowl with half an egg and a piece of nori. Serve immediately.