Preheat the oven to 200°C/180°C fan/gas mark 6. Whisk together the miso, honey, mirin, garlic and 2 tbsp soy until you have a smooth paste. Put the cod loins on a baking tray lined with baking parchment paper. Spread the paste across the top of the cod and bake in the oven for 12-15 minutes.
Meanwhile, heat the oil in a large frying pan or wok. Stir-fry the pak choi and chilli for 3-4 minutes, until wilted. Splash over the remaining soy. Cook the broccoli rice according to the instructions on the packet. Stir through the coriander and season with black pepper.
To serve, divide the broccoli rice between four shallow bowls. Top each with a fillet of cod and the pak choi, then scatter over the spring onions.