Heat a grill to high. Following the shape of the peppers, cut them lengthwise into wide, flat panels and discard ribs and seeds. Place peppers, skin side down, on the grill and cook until the skin is charred and the peppers are tender but not mushy, about 10 minutes.
Remove peppers from grill; when cool enough to handle, peel off skin and cut peppers into 2-inch-wide pieces. Transfer to a bowl, toss with oil, and season with salt.