Quarter bell peppers lengthwise and discard stems, seeds, and ribs. Arrange peppers, skin sides up, on rack of a broiler pan and broil about 2 inches from heat until skins are blistered, 8 to 12 minutes. (Alternatively, lay whole peppers on their sides on racks of burners of a gas stove and turn flames on high. Char peppers, turning them with tongs, until skins are blackened, 5 to 8 minutes.)
Transfer roasted peppers to a bowl and let stand, covered, until cool enough to handle. Peel peppers and cut each quarter lengthwise into 2 or 3 strips. Thinly slice garlic and in a bowl toss with peppers, oil, and salt to taste. Marinate peppers, covered and chilled, at least 3 hours and up to 3 days.
