Preheat the broiler.
If using fresh bell peppers, cut the bell peppers in half and lay them flat on a rimmed baking sheet. Broil for 12 minutes, or until blackened. Let cool for 2 minutes, and then place the peppers in a brown paper bag. Secure the bag with a rubber band or twist tie and let the peppers steam for 10 minutes. Remove from the bag and rub the charred skin off with your fingers. Run the peppers under water to ensure all the skin is removed. Discard the seeds and dice the peppers.
In a large bowl, combine the roasted peppers, tomatoes, Gluten-Free Herbed Croutons, arugula, basil, parsley, and cucumber, if using.
In a separate bowl, whisk together the oil, vinegar, shallot, garlic, and salt and black pepper to taste.
Drizzle the dressing over the bell pepper mixture and gently toss to combine.
Serve at room temperature.