Prepare a medium-high grill fire.  Grill the bell peppers, turning occasionally, until the skin chars all over, 15 to 20 min.  Or roast the peppers in a 500°F oven until blackened all around. Put the charred peppers in a heatproof bowl, cover with plastic wrap, and let sit until cool enough to handle about 30 minutes.

Meanwhile, in a medium bowl, combine the balsamic vinegar, olive oil, the chopped thyme & parsley, salt, and about 5 grinds of pepper.  Mix well.

Remove the pepper skins and seeds.  Cut the peppers into thin strips.  Add the peppers to the vinegar mixture and let them marinate for at least 1 hour and up to 3 days.  Allow the pepper strips to return to room temperature before serving.