Preheat the oven to 180°C. Heat 1 tablespoon of the oil in a large, deep frying pan, cook mushroom and spring onions over a medium heat for 5 minutes until mushroom is tender. Stir in spinach and cook, stirring, for 2 minutes, until wilted.
Transfer to a large bowl, using a slotted spoon to drain off any excess moisture from the spinach. Add the breadcrumbs, Parmesan and pepper and toss well.
Flatten chicken between two sheets of plastic wrap. Spread 2 tablespoons of spinach filling onto each piece of chicken, to about 1 cm from the edges. Start at a narrow end, roll up and secure each pocket with cocktail sticks or kitchen string.
Clean frying pan, add remaining oil and set the pan over a high heat. Add the pockets, seam side down first, and cook for 6 minutes, or until browned all over.
Place the pockets in a shallow ovenproof dish and pour in the hot stock. Cover and bake for 15 to 18 minutes, or until the chicken is cooked through.
To serve, remove cocktail sticks or string from pockets and cut chicken diagonally into 1-cm slices. Serve hot, drizzled with cooking juices on pasta with salad greens.
Cooking the pockets seam side down first seals them closed and prevents the filling from falling out.