Heat the oil in a small saucepan until warm. Add remaining ingredients and heat for about 2 minutes over a low heat.
Remove from heat and pour into a heatproof jug. Cover and rest in a cool place to steep for 24 hours. (If weather is particularly hot, place in the fridge.)
Strain through a fine mesh sieve into a jar, screw on the lid and refrigerate until ready to use.
Blackening spice mix
Mix all ingredients together and store in an airtight container.
Fish and mushrooms
Heat 2 tablespoons of the oil in a large frying pan over a medium heat. Rub fish fillets with the blackened spice mixture and place in the frying pan. Pan-fry for 3-4 minutes, turning once, for thinner fillets (6 minutes for fillets about 2.5cm thick). Transfer to a plate to keep warm.
Wipe out frying pan if a little too blackened, then pour in the remaining oil. Add the mushrooms and pan fry until lightly browned. Sprinkle over sesame oil and ginger and pan fry until aromatic.
Serve fish and mushrooms drizzled with a little coriander oil. Serve with a green salad with a few small radishes.