Start by preparing the eggplant. Place the cut eggplant pieces in a colander, sprinkle with salt, and let them sit for about 30 minutes to draw out excess moisture. Rinse and pat dry with paper towels.

In a large bowl, combine the cornstarch, salt, and black pepper. Toss the dried eggplant pieces in the cornstarch mixture until evenly coated.

Heat the vegetable oil in a large skillet or wok over medium-high heat. Once hot, add the eggplant in batches, frying until golden brown and crispy, about 4-5 minutes per batch. Remove and drain on paper towels.

In the same skillet, reduce the heat to medium and add the minced garlic and ginger. Sauté for about 30 seconds until fragrant.

In a small bowl, whisk together the soy sauce, rice vinegar, sugar, sesame oil, and red pepper flakes (if using). Pour this sauce into the skillet and bring to a simmer.

Add the crispy eggplant back to the skillet, tossing to coat in the sauce. Cook for an additional 2-3 minutes until heated through.

Remove from heat and garnish with sliced green onions before serving.