For the salmon goujons, whisk together the flour, egg, milk and enough sparkling water to make a batter with the consistency of double cream (you may not need all of the water).
Half-fill a deep saucepan with the vegetable oil and heat until a small cube of bread dropped in sizzles and turns golden-brown in 30 seconds (CAUTION: hot oil can be dangerous. Do not leave unattended). Dip the salmon strips into the batter and deep-fry, in batches, in the oil for 1-2 minutes, or until golden-brown. Remove with a slotted spoon and drain on kitchen paper. Repeat until all the salmon strips are cooked.
For the sweet potato chips and garlic, heat the oil in an ovenproof frying pan and gently fry the sweet potato and garlic for 3-4 minutes, then transfer to the oven to cook for 10-12 minutes, or until the chips are tender and golden-brown.
To serve, pile the salmon goujons on a serving plate alongside the sweet potato chips and garlic. Garnish with a slice of lemon.