Toss the peppers with 1 tablespoon olive oil, salt and pepper. Roast the peppers until their skins are wrinkled and they are charred, about 30-35 minutes flipping halfway through cooking.
Place the peppers in a bowl and cover with plastic wrap. Let the peppers steam for 10-15 minutes. Peel off the skins and remove the stems. Split the peppers on half and remove the seeds.
With the peppers in a bowl, stir in the remaining olive oil, balsamic vinegar and red pepper flakes.