For the peas, heat the oil in a frying pan over a medium heat and fry the onion for 1-2 minutes. Add the chilli and stir well.
Add the pancetta or bacon and cook for 8-10 minutes until golden-brown and crisp.
Add the peas to the pan, give the pan a good shake and cook for a further 2-3 minutes.
For the chips, place the vegetable oil into a deep, heavy-based saucepan and heat until a small cube of bread sizzles and turns golden when dropped into it. (CAUTION: hot oil can be dangerous. Do not leave unattended.)
Carefully place the potatoes into the hot oil. Cook for about ten minutes, until golden-brown and crisp. Remove from the pan using a slotted spoon and drain on kitchen paper.
Sprinkle with the rosemary and a little salt.
For the fish, sift the flour, cornflour, five-spice powder and salt into a bowl and stir.
Gradually pour in the soda water, whisking continuously, to make a smooth batter the consistency of thick double cream.
Using tongs, dip the fish fillets into the batter to coat completely, shaking off any excess.
Place the fish into the hot oil that the chips were cooked in. Cook for 4-5 minutes, turning carefully from time to time.
When golden-brown and crisp, remove the fish from the oil with a slotted spoon and drain on kitchen paper. Sprinkle with salt, to taste.
To serve, place the fish onto plates with the chips and peas and lemon wedges.