In a small bowl, mix together 1½ tbsp sesame oil with the soy sauce, sugar, ginger and chilli. Set aside. Put the flour in a shallow bowl and season with freshly ground black pepper. Pat the fish dry with kitchen paper and dust the skin with the flour.
Heat ½ tbsp sesame oil in a large frying pan over a medium heat. Fry the coley, skin-side down, for 4 minutes, until crisp and golden. Turn and fry for a further 2 minutes, until cooked through. Add the sesame seeds to the pan for the last 2 minutes until toasted. Remove the fish and sesame seeds and keep warm.
Heat the remaining oil in the frying pan and add the stir-fry mix and coriander. Stir-fry for 1 minute, then transfer to a bowl and leave to cool slightly before tossing with the spinach and most of the dressing. Serve the fish and the stir-fried veg garnished with the toasted sesame seeds, with the remaining dressing on the side.