Preparation Prepare a grill for high heat. Clean and lightly oil grates. Grill peppers, turning occasionally, until skins are blackened and blistered all over, 15–20 minutes. Transfer to a large bowl, cover with a lid, plate, or plastic wrap, and let cool. Remove skins and seeds from peppers; discard. Tear flesh into about 2"-wide strips. Transfer to a clean large bowl and toss with olive oil, vinegar, salt, and red pepper flakes. Let marinate at least 30 minutes. Do Ahead: Peppers can be marinated 5 days ahead. Transfer to an airtight container and chill.
Preparation Prepare a grill for high heat. Clean and lightly oil grates. Grill peppers, turning occasionally, until skins are blackened and blistered all over, 15–20 minutes. Transfer to a large bowl, cover with a lid, plate, or plastic wrap, and let cool. Remove skins and seeds from peppers; discard. Tear flesh into about 2"-wide strips. Transfer to a clean large bowl and toss with olive oil, vinegar, salt, and red pepper flakes. Let marinate at least 30 minutes. Do Ahead: Peppers can be marinated 5 days ahead. Transfer to an airtight container and chill.