Whisk the water, soy sauce, sugar, cornstarch, and red pepper flakes together in a small bowl until the sugar and starch are fully dissolved.

Combine a teaspoon of the oil with the garlic and ginger in a small bowl and set aside.

Heat the remaining oil in a 12-inch nonstick skillet over high heat until it is shimmering but not smoking. Add the eggplant and bell pepper and cook, stirring frequently, until the vegetables are well browned and tender, 8 to 10 minutes.

Push the vegetables to the edge of the skillet to clear the center. Add the garlic-ginger mixture to the center and cook, mashing it into the skillet with a spatula until it becomes fragrant, about 30 seconds.

Stir the garlic mixture into the surrounding vegetables. Give the sauce a final whisk to recombine any settled starch, then pour it into the skillet.

Cook, stirring constantly, until the sauce has thickened and coated the vegetables, about 30 seconds.

Remove the skillet from the heat and stir in the basil and scallions. Serve hot over steamed rice.