Cut eggplants into 4 pieces lengthwise, then cut each piece into rough 2-inch strips.
Stir 1 teaspoon salt into a large bowl of water, and submerge eggplant pieces (cover with a plate to ensure pieces are submerged). Leave to soak for 15 minutes.
Drain and pat dry eggplant with paper towel, then toss in 1 tablespoon cornstarch, ensuring eggplant is evenly coated.
In a small bowl, mix together soy sauce, sugar and remaining 1 teaspoon cornstarch until combined (use a whisk to break down cornstarch lumps).
Heat 2 tablespoons oil in a large skillet or frying pan on medium high heat. Add eggplant in a single layer and fry until golden - 6-8 minutes - flipping frequently. (If skillet isn't large enough, do two batches.)
Transfer eggplant to a plate. Add remaining ½ tablespoon oil to skillet. Sauté garlic and ginger for 30 seconds on medium heat.
Add sauce and cooked eggplant to skillet, and cook - stirring - for one minute to allow sauce to thicken.