Preheat oven to 220°C (or 200°C fan forced). If trout portions contain skin, remove and set aside. Line a large baking try with baking paper.
Bring a saucepan of salted water to the boil and add baby spinach. Blanch for 1 minute and remove. Drain well in a colander. Immediately place colander in a bowl of iced water until cold. Drain. Squeeze out all excess moisture from spinach and pat dry with paper towel. Finely chop (or shred) spinach and set aside in a small bowl.
In separate bowl, make your dill mustard. Add lemon rind, mustard, aioli, honey, chives, tarragon and dill. Mix with fork. Add 2½ tablespoons to the spinach mixture.
Cut each sheet of pastry in half. Place one portion of ocean trout on one side of pastry. Lightly season with salt and pepper. Top each one with a ¼ of the spinach mixture.
Fold over each pastry parcel and seal the edges, by folding the edges over. Gently slice 3 small slits in the top of each parcel, to allow steam to escape whilst cooking.
Brush the tops of each parcel with the beaten egg. Place the trout parcels on the lined oven trays. Bake in oven for 25 minutes or until golden and puffed.
Drizzle parcels with dill mustard and garnish with fresh dill. Serve with fresh side salad.