Combine all the ingredients in a small container. If using sugar, let stand until it’s dissolved. Otherwise, whisk together.
Stem the eggplants and cut in half lengthwise.
Whisk the marinade again just before pouring ⅓ cup of it into a wide skillet. Heat lightly, then arrange the eggplants cut side down in a single layer.
Cover and cook over medium heat until nearly tender and golden brown on the underside. Add more marinade as needed if the skillet gets dry. The time this will takes varies depending on the eggplant variety used, so check frequently.
Flip the eggplants over and cook until tender but not overdone. Pour a little more marinade into the skillet, turn the heat up to high, and sear the eggplants’ underside for a minute or so.
Remove to a plate and garnish with the scallions. Serve hot or at room temperature, and pass around any unused portion of the marinade for individual servings, if you’d like, or save for another use.