Preheat the oven to 400 degrees F. Line a rimmed sheet pan with parchment paper.
Drain the peeled tomatoes and reserve the liquid. Place the tomatoes evenly on the lined sheet pan. Spread the mirepoix on the sheet pan with the tomatoes. Drizzle the tomatoes and mirepoix with oil, and sprinkle with red pepper flakes and salt.
Bake until the mirepoix is lightly browned, about 30 minutes. Allow to cool slightly.
Place the cooked tomato mixture in a blender using tongs, along with the vegetable broth, bread and reserved tomato juice, Blitz until smooth and transfer to a medium soup pot.
To serve immediately, place the pot over medium heat. Warm the soup through and season with salt and pepper to taste.
To freeze, divide the soup evenly among four 16-ounce mason jars. Leave at least 1 inch of space at the top of each jar to prevent cracking. Screw on lids and freeze. To serve, place jars in a saucepan filled with cold water over medium heat until warm. Or, place a frozen jar in your lunchbox and reheat in the microwave for an on-the-go lunch.