Bring 3 cups water to a boil
Combine the shallots, cucumber, carrot and 1 tablespoon salt in a medium heatproof bowl
Carefully pour over the boiling water
Stir to mix evenly then let stand for 20 minutes
Drain the vegetables in a colander, pressing them to remove excess liquid, then transfer them to a bowl
Add the vinegar, sugar, chile and the remaining 1 teaspoon salt
Stir until the sugar and salt dissolve then refrigerate until ready to use, at least 10 minutes and up to 1 hour