Preheat barbecue to medium. Trim ends off eggplants. Slice each lengthwise into 3 long slices.
Whisk 1/4 cup oil with vinegar, salt and garlic in a large bowl. Add tomatoes and capers and toss to coat. Season with pepper.
Brush eggplant slices with remaining oil. Oil grill, then barbecue eggplant, lid closed, flipping halfway through, until cooked but still firm, 3 to 4 min per side. Chop into large chunks. Stir into tomato mixture.