Bring a medium saucepan of water to the boil for the noodles. Halve the carrot lengthwise, then thinly slice on an angle. Thinly slice the spring onion. Crush or finely chop the garlic. Peel and finely grate the ginger (remove soft ginger skin easily - simply scrape with a teaspoon and lift off).
Step 2 — Prep sauce
Combine the mirin, 2½ tbs soy sauce, 2 tbs white vinegar and 125ml (½ cup) water in a bowl.
Step 3 — Cook fish
Heat 2 tsp oil in a medium deep frypan over medium-high heat. Cook the carrot, stirring, for 3-4 mins until softened. Add the garlic, ginger and half the spring onion and cook, stirring, for 1 min or until fragrant. Stir in the sauce, then add the fish to the pan and bring to a simmer. Reduce the heat to low and cook, covered, for 8-9 mins until the fish is just cooked.
Step 4 — Stir-fry vegetables
While the fish is cooking, thinly slice the cabbage and pak choy. Heat 2 tsp oil in a medium frypan over high heat. Stir-fry the cabbage for 2-3 mins until slightly charred. Add the pak choy and stir-fry for 1-2 mins until tender.
Step 5 — Cook noodles
Meanwhile, cook the noodles in the pan of boiling water for 2 mins or until tender. Drain, then rinse under hot water to prevent the noodles from sticking.
Step 6 — Get ready to serve
Carefully remove the fish from the pan and cover to keep warm. Increase the heat to high and cook the sauce for 2 mins or until slightly reduced. Add the noodles and vegetables to the sauce and toss to coat. Flake the fish into large chunks. Divide the noodle mixture and fish among bowls. Scatter with the sesame seeds and remaining spring onion to serve.