Heat the oil in a small saucepan over medium heat. Add the ginger, garlic and red chili flakes and cook until soft, 3 to 4 minutes. Remove from the heat and whisk in the hoisin, vinegar and soy sauce until combined and then strain, reserving the sauce.
Heat grill to high.
Brush eggplant slices on both sides with the oil and season with salt and pepper. Place the slices on the grill and grill until golden brown and slighty charred, 4 to 5 minutes. Brush with some of the glaze, turn over and continue grilling just until cooked through, brushing with more of the glaze, 3 to 4 minutes longer. Remove from the grill and brush with the remaining glaze. Transfer to a platter and sprinkle with the cilantro.