Place the dried mushrooms in a heatproof bowl, pour over boiling hot water and leave to soak for 30 minutes until softened. Drain and squeeze out the excess water. Remove and discard the stems, and finely chop the caps.
Spray a large wok or frying pan with cooking spray and heat until smoking. Add the mushrooms and stir-fry for 1–2 minutes, then stir in the soy sauce and five-spice powder. Remove from the pan and leave to cool for 10 minutes. Wipe the pan clean with kitchen paper.
Place the bean sprouts, spring onions, carrot and ginger in a bowl, add the mushroom mixture and oyster sauce and season well with salt and white pepper. Mix well.
Lay 2 spring roll wrappers on top of each other. Spoon 2 tablespoons of the filling in the centre. Brush each corner with cornflour paste. Fold the 2 opposite corners over the filling, then roll the wrapper up tightly from one of the other corners. Seal the roll with a little beaten egg yolk. Repeat with the remaining wrappers and filling.
Arrange the rolls on a baking sheet lined with nonstick baking paper, lightly spray with cooking spray and bake in a preheated oven, 200°C (400°F), Gas Mark 6, for 12–15 minutes, or until lightly golden and crisp. Serve immediately with sweet chilli sauce for dipping.