Trim the eggplant and use a peeler to remove strips of the eggplants’ skin to strip the eggplant lengthwise. Cut eggplant in 3/4-inch disks and then quarters. Soak eggplant pieces in cold water for 5 minutes to remove any bitterness. Drain and pat eggplant dry with paper towels (steps two and three can be prepared while the eggplant is soaking).
Combine the soy sauce, mirin, sugar, and rice vinegar in a large glass, ceramic, or metal serving bowl and set aside.
Rinse, drain, and chop the lettuce into bite-sized pieces. Place a serving of lettuce onto each dinner plate or bowl. Set aside.
In a large skillet, heat 2 tablespoons of olive oil. When hot, add the eggplant pieces and stir fry for about 5 minutes (until eggplant pieces are tender in the middle).
Place the cooked eggplant directly into the bowl of sauce; add ginger, chillies, scallions and optional garlic and combine.
Serve eggplant on chopped lettuce with warm sauce and shredded scallions on top for garnish.