Slice bitter melon lengthwise, remove seeds with a spoon then divide each half in three. Slice each third into julienne pieces (like matchsticks). Boil 2 minutes.
Divide eggplant in three. Slice each third into julienne pieces. Boil in water for 2 minutes only; do not overcook. Julienne the carrot also.
Mix bittermelon, eggplant, carrot, garlic, green chillies and onion in a large bowl with a cover.
In a non-reactive saucepan bring vinegar, water, sugar, ginger and salt to a boil then stir until the sugar has dissolved completely. Cool and set aside.
Pour vinegar mixture into the bowl making sure vegetables are covered.