Heat the oil in a large frying pan over medium-high heat. Add the onion, garlic and ginger and cook, stirring, for 3 minutes or until onion softens. Add the chicken mince and cook, stirring with a wooden spoon to break up any lumps, for 3 minutes or until mince changes colour.
Stir in the sweet chili sauce and soy sauce, and bring to the boil. Remove from heat. Stir in the basil and chili.
Meanwhile, place the noodles in a medium heatproof bowl and cover with boiling water. Set aside for 2 minutes or until noodles soften. Drain. Use sharp kitchen scissors to cut the noodles into 2cm lengths. Add the noodles and carrot to the chicken mixture, and stir until well combined.
Place a pastry sheet on a clean work surface. Spoon 2 tablespoonfuls of chicken mixture diagonally across the centre of the pastry sheet, leaving a 4cm border at each end. Brush the corners and sides with water. Fold in the ends and roll up firmly to enclose filling (you should have a 10cm-long spring roll). Repeat with the remaining pastry and chicken mixture.
Add enough extra oil to a large heavy-based saucepan to reach a depth of 10cm. Heat to 180°C over high heat (when oil is ready a cube of bread will turn golden brown in 15 seconds). Add half the spring rolls and deep-fry for 3-4 minutes or until golden brown. Use tongs to transfer to a plate lined with paper towel. Repeat with the remaining spring rolls, reheating oil between batches.
Combine the mayonnaise, sweet chili sauce and lime juice in a serving bowl. Taste and season with salt.
Arrange the spring rolls on a serving platter and serve immediately with sweet-chili mayonnaise.