Preheat oven to 400°F (200°C).
Arrange tomatoes cut-side up on a baking sheet lined with parchment.
Scatter onion, garlic, and bell pepper around the tomatoes.
Drizzle with olive oil and season generously.
Add herbs if using.
Roast for 35–45 minutes, until tomatoes are blistered and edges are caramelized.
Remove from oven and let cool slightly before blending.
