Add 3/4 cup of water and the cornstarch to a medium bowl. Whisk to combine. Add the soy sauce, brown sugar, hoisin, vinegar, Chinese five spice, garlic powder and red pepper flakes. Whisk to combine and set aside.
To prepare the eggplant, slice the ends off of an eggplant. Slice into thirds horizontally, so you have 3 cylinders. Slice each cylinder lengthwise into quarters, so you have sticks. Repeat with remaining eggplants.
Heat about 2 tablespoons of oil in a large nonstick skillet over medium high heat. Add half of the eggplant, season with salt and pepper, and cook until charred and softened, about 7 – 10 minutes. Transfer to a bowl and repeat with remaining half.
Deglaze the pan with 2 tablespoons of water, scraping up the brown bits on the bottom of the skillet. Pour into the bowl with the eggplant.
Lower the heat to medium and add about a teaspoon of oil to the skillet. Add the garlic and scallions and sauté for 30 – 60 seconds.
Give the sauce mixture a good whisk and pour into the skillet. Let simmer until thickened, about 1 – 2 minutes.
Add the eggplant and chili oil to the skillet. Season with salt. Stir to combine and let cook for 5 – 7 minutes so the eggplant can absorb all the flavors.