Heat the oil in a medium suacepan and fry the onion until soft and transparent. Add in the rice and spinach; cook for a further minute until spinach has wilted. Sauté the garlic until fragrant (about 30 seconds). Season with salt and pepper.
Add water and stock powder to the pan. Bring to a boil, stirring occasionally to combine all ingredients.
Reduce heat to low, cover and gently simmer for a further 12-15 minutes, or until the rice is cooked through.
Remove from heat and stir through lemon juice and parsley. Set aside and let cool.
Preheat oven 410°F (210°C). Line a baking tray with baking/parchment paper.
Cut pastry sheets in half to make 2 rectangles per sheet.
With the shorter edge in front of you, spoon 1/4 of the rice and spinach mixture on the lower half of the pastry, leaving a 1-inch (2-cm) border around the edges.
Lay the salmon fillet on top of the rice mixture and brush the border/edges of the pastry with water.
Fold empty side of pastry over to envelope salmon, and seal the edges firmly with a fork. Transfer parcel to prepared baking sheet/tray and repeat the same steps with reamining pastry, rice mixture and salmon fillets until all parcels have been done.
Brush parcels with whisked egg and bake for 20 - 25 minutes or until golden brown.
Slice each parcel in half and serve warm.