Turn on broiler. Place peppers on a rimmed baking sheet and place under the broiler. Broil for 3 to 5 minutes per side, or until charred.
Remove from oven and place in a paper bag or bowl covered tightly with plastic wrap. Allow steam to loosen bell pepper skin for about 5 minutes.
Turn your oven to 400F. Place tomatoes, onions, and garlic cloves on two large rimmed baking sheet. Drizzle with olive oil and salt. Roast for 20 minutes.
While tomatoes are roasting, remove peppers from bag/bowl and peel skin. Cut bell peppers, removing the core and seeds.
In a large pot, add peppers. Remove roasted vegetables from the oven. Squeeze garlic out of the skins of the cloves.
Add tomatoes, onions, and garlic to the pot. Stir in red wine vinegar, olive oil, and vegetable broth. Using an immersion blender, pulverize until smooth.
Bring to a slow boil and stir. Reduce to a simmer and season with red pepper flakes and salt.
While soup is simmering, slice 1/4 of baguette into cubes for croutons. Toss with additional olive oil, salt, and dried oregano.
Slice remaining baguette in half. Drizzle with additional olive oil. Season with salt and dried oregano.
Place both croutons and sliced baguettes on a rimmed baking sheet. Place under a broiler for 1 minute, watching carefully. Remove and flip croutons. Return to broiler for 1 more minute, watching carefully to avoid burning.