Preheat broiler. Halve peppers lengthwise, discarding stems and seeds. Arrange peppers, cut sides down, in 1 layer in a large shallow baking pan. Line the baking sheet(s) with foil or parchment paper for easy clean-up.
Broil peppers 4 to 5 inches from heat until well charred (peppers will not char evenly, especially at ends), 20 to 25 minutes.
Transfer peppers to a bowl and cover with a towel, then let steam in the bowl for 20 minutes. When peppers are cool enough to handle, peel off skin.
Notes
If saving for later, pour the oil over the peppers. Place in an air tight container and refrigerate for up to 2 weeks.