Preheat grill pan or large nonstick skillet over medium high heat.
Brush endive on both sides with oil, season with salt and pepper then grill until dark around edges and endives are tender; about 3 minutes on each side. Arrange grilled endives on platter. Sprinkle the endive with white wine vinegar. Keep a finger over the top of bottle to control the flow if the bottle does not have a jigger top. Arrange walnut bits and grapes around the platter and serve.
Recipe courtesy of Rachael Ray