Make the teriyaki sauce. Put the mirin or sherry in a saucepan, bring to the boil and simmer for 2 minutes or until reduced by half. Add the soy sauce and stock, stir and remove from the heat.
Line a grill pan with foil, spray with oil and arrange the bass fillets on the foil. Brush the fish with the teriyaki sauce and cook under a preheated hot grill for 5—6 minutes, basting often with the sauce.
Meanwhile, cook the noodles in lightly salted boiling water for 3 minutes or according to the instructions on the packet. Drain and stir in the sesame oil, chives and spring onions.
Serve the bass on a bed of piping hot noodles and drizzle over any juices from the grill pan.