Preheat grill to medium high. Brush eggplant, peppers and onions on both sides with 1/4 cup of the oil and season with salt and pepper to taste. Grill for 3 to 4 minutes on each side, until lightly golden brown and almost cooked through. Remove vegetables from grill and cut into 1/2-inch dice. Combine eggplant, peppers and onions in a medium bowl. Add remaining ingredients inluding the remaining 2 tablespoons of olive oil and season with salt and pepper, to taste.