Cut fish into 2cm thick strips. Cut the pancetta and bamboo into 5mm thick matchsticks. Cut 2 spring onions in pieces about the same size, keeping the white and green parts separate. Finely slice the remaining spring onion and reserve to use as a garnish. Finely chop the ginger garlic and chilli and slice the mushrooms.
Heat a wok until smoking. Add half the peanut oil and when hot, quickly stir-fry the fish in two batches until golden, about 1-2 minutes per batch. Remove and drain on a paper towel.
Wipe the wok clean. Heat remaining peanut oil until just smoking. Stir-fry the pancetta, ginger, garlic, chilli, mushrooms, bamboo and the white spring onion pieces until fragrant, about 2 minutes. Return snapper to the wok with chicken stock, oyster sauce, soy sauce and sugar. Stir-fry together until the sauces are combined (about 1 minute), then fold through the green pieces of spring onion.
Remove from heat, add pepper to taste and check seasoning. Spoon into a large share bowl, scatter with finely sliced spring onions and serve.