Slice the eggplants lengthwise into quarters, then cut them into 2-inch segments. In a large cast-iron skillet over high heat, warm 2 tablespoons of oil. Add half of the eggplant and cook, stirring occasionally, until the pieces soften and develop a golden-brown color in spots, about 4 to 5 minutes. Transfer to a large bowl. Repeat with another 2 tablespoons of oil and the remaining eggplant. Once cooked, cover the eggplant to retain warmth and set aside.

In a small bowl, whisk together the hoisin sauce, soy sauce, and plum sauce until well combined. Set the mixture aside.

Heat the remaining 1 tablespoon of oil in the same skillet over high heat. Add the jalapeño slices and onion wedges, stirring frequently, and cook until they soften slightly, about 4 to 5 minutes. Stir in the minced garlic and ginger, cooking for another 30 seconds to 1 minute until aromatic.

Return the cooked eggplant to the skillet, then incorporate the onion mixture and fresh basil. Pour in the prepared sauce, stirring until everything is evenly coated. Serve immediately while warm.