Preheat a grill, a grill pan, or a dual-contact electric grill over medium-high heat.
Trim the eggplant's edges and slice it crosswise into ½-inch-thick rounds. You should get about 12 slices.
In a small bowl, whisk the olive oil, vinegar, salt, pepper, and garlic powder.
Brush the eggplant slices with the mixture on both sides. Set aside any remaining marinade.
Grill the eggplant slices until golden brown and fork-tender, about 5 minutes on each side. In my dual-contact electric grill, I grill for 5 minutes on one side, then 2 minutes on the second side.
Brush the eggplant slices with the remaining marinade and serve.
