Slice the eggplant and zucchini
lengthwise into slice 1/2-inch thick slices.
Peel the onion and cut into rings
3/4-inch thick.
Use a pastry brush to coat vegetables
on both sides with olive oil.
Sprinkle with salt and pepper and lay
on the hot grill, closer to the edges (avoid placing over direct
heat).
Grill for about 5 minutes on each
side, perhaps longer according to the heat of your grill, until the
vegetables are softened and dark brown but not black.
Remove to a serving platter and
drizzle with more olive oil and some balsamic vinegar, if desired.