When choosing peppers for grilling, pick ones that feel heavy for their size with thick walls. Grilled peppers make a great sandwich addition -- and lend flavor to any number of dishes -- so consider making a double batch.
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.