Preheat the oven to 350°F Spray a large rimmed baking sheet with nonstick spread.
Mix the tomatoes, olives, capers, garlic, red pepper flakes, and 1 tsp of the oil in a bowl. Spread the bell peppers, skin side down, on the baking sheet. Spoon the tomato mixture over them. Cover loosely with foil and roast 30 minutes. Uncover and roast until the peppers are tender, about 15 minutes. Let the pepper mixture cool. Transfer to an airtight container and refrigerate up to two days.
To serve, transfer the salad to a medium bowl and let come to room temperature, about 1 hour. Whisk the remaining 2 tsp oil, the vinegar, and salt in a small bowl. Drizzle over the salad and sprinkle with the basil or parsley.