Heat oil in a heavy-based pan, add pork cubes and turn until brown. Add garlic and onion and cook, stirring to separate onion rings until transparent. Remove from heat.
To make caramel, mix sugar with water in a separate saucepan and stir over low heat until sugar dissolves. Bring to the boil then turn down to simmer, still stirring, until liquid is golden. Take pot off heat and carefully add fish sauce and lime juice. Return to heat, stirring quickly to remove any lumps, until the sauce reduces a little.
Quickly return pork, garlic and onions to reheat, ad chili and five spice and then caramel. Cook for 1 minute, stirring until combined. Transfer to serving dish and sprinkle spring onions on top.
