Cut the pork into 1/4-inch-thick slices, then cut the slices into 1/4-inch-thick slivers. Toss with 2 tablespoons cornstarch.
In a large skillet, heat 1 1/2 tablespoons oil over medium-high heat. Add the scallions and garlic; cook, stirring, until golden, about 2 minutes. Add the pork and cook, stirring, until just no longer pink, 3 minutes. Transfer to a bowl.
Add the remaining 1 1/2 tablespoons oil to the skillet, add the eggplant and cook, stirring, until slightly softened, about 3 minutes. Add the bell pepper and cook, stirring, until crisp-tender, about 2 minutes. In a small bowl, stir together the chicken broth, stir-fry sauce and remaining 1 tablespoon cornstarch; pour over the vegetables and cook, stirring, until the sauce is thickened, 1 to 2 minutes. Return the pork mixture to the skillet and stir until heated through, 1 to 2 minutes.