In a bowl, combine the fish sauce, garlic, curry powder, salt, and the 1 teaspoon of sugar.
Add the chicken meat to coat. In a small skillet, mix the remaining 2 tablespoons of sugar with 1 tablespoon of the water and cook over high heat, stirring until the sugar is dissolved. Cook without stirring until a deep amber caramel forms.
Remove from the heat and stir in the remaining 2 tablespoons of water and then transfer to a bowl.
Heat a wok over high heat and add the oil and heat until shimmering.
Add the lemongrass, shallot, and chilies and stir-fry until fragrant.
Add the chicken and caramel and stir-fry until the chicken is cooked through and the sauce is slightly thickened.
Transfer to a bowl and top with the scallion. Serve with steamed white rice.