Rinse cod, pat dry and cut to fit the pan. Season with salt and pepper and drizzle with lemon juice. Place in an oiled steamer.
Boil fish stock in a pot, add steamer basket, cover and steam cod about 8 minutes. Remove and let cool.
Meanwhile, Soak 7 leaves of gelatine in cold water. Combine cream cheese, mustard, mustard seeds and lemon juice. Season with salt and pepper. Beat cream until stiff and fold into cream cheese mixture. Dissolve gelatine in a small saucepan over low heat, stir in 3-4 tablespoons of cream cheese mixture, then stir into remaining cream cheese mixture.
Line a pan with plastic, add cream cheese mixture and smooth. Chill for 2 hours.
Soak 3 leaves of gelatine in cold water. Rinse cilantro, remove leaves and chop. Squeeze out gelatine and dissolve in 3-4 tablespoons of fish stock in a saucepan over low heat, then stir into remaining gelatin and season with salt and pepper. Sprinkle half the cilantro onto the cream cheese mixture. Add cod and top with remaining cilantro and gelatine. Chill for 4 hours.
Slice and serve.