Prepare the wrappers according to the packaging if needed. In a medium bowl mix together all the filling ingredients, making sure that the onions and gherkins are fine enough not to piece the spring roll casing. If using square wrappers, place the wrapper with a point towards you. Double the wraps up so the filling does come out when they go into the oil. Use around two tablespoons of mix and pack it in tightly. Start rolling the spring roll up, making sure the casing is wrapped tightly around the filling. Fold in the sides and use a little egg wash on the final point to ensure it sticks. Repeat with the other three spring rolls.
Ensure the pan is filled with a good couple of inches of frying oil. Heat up to 350°F, you want to ensure the meat is cooked through before the casing is too crisp, so you may have to adjust the temperature slightly as you go along. Fry for around 4-5 minutes and then turn using tongs and fry again on the other side for the same amount of time.
Blot on kitchen towel and serve with ketchup and sweet chilli sauce.