In a small bowl, mix together 1½ tablespoons of the sesame oil, 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 tablespoon of the 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, to toast. 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 let 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.