Madhur Jaffrey’s recipe for this dish in Curry Easy contains 2tbsp of Dijon mustard. Having tried it, and much as I like mustard, I would be inclined to halve the quantity, but to increase her spice measurements.
Jaffrey recommends leaving the fillets in a rub of the dry spice ingredients, before adding the mustard, oil, and coriander leaves. If you have no opportunity for advance preparation, you can assemble the sauce in one receptacle.
1tsp cumin seeds
1/4tsp coriander seeds
1/4tsp cayenne pepper
1tbsp smooth Dijon mustard
1tbsp olive or sunflower oil
2tsp lemon juice
2tbsp chopped fresh coriander
2 salmon fillets
Toast the cumin and coriander seeds in a small saucepan over a gentle heat. Ground them in a mortar, and add the turmeric, cayenne, salt, mustard, oil, lemon juice, and fresh coriander.
Put the salmon fillets in an oven dish, and smear the sauce over them. Place under the grill, until the top browns slightly. Transfer to a gas mark 6/200C oven, and bake for 8 to 10 minutes, or until the fish is cooked through.