Boil the eggs for 7 mins, then plunge into cold water. Heat 1 tbsp oil in a frying pan, add the mushrooms and a pinch of seasoning and cook, stirring occasionally, for 8-10 mins until golden. Add the rice, dill, lemon zest and juice, capers and some more seasoning, then remove from the heat.
Line a baking sheet with parchment. Put two sheets of pastry next to each other on the tray, slightly overlapping in the middle. Brush with some oil and top with another two sheets, then repeat with two more sheets. Butterfly the salmon by cutting through the side, but not all the way through, so you can open it like a book. Heat oven to 180C/160C fan/gas 4.
Place the salmon on the pastry and stuff with the rice mixture. Peel and slice the boiled eggs and arrange on the rice. Close up the salmon fillet, season and wrap with the pastry to form a parcel. Scrunch the remaining pastry sheet over the top, drizzle with a little more oil and bake for 40 mins. Serve with lemon wedges and dressed salad leaves.