01 - Preheat oven to 390°F.
02 - Arrange tomatoes, red onion, garlic, and red bell pepper in a large baking dish. Drizzle with 2 tablespoons olive oil, sprinkle with oregano, salt, pepper, and red pepper flakes if using; toss to coat evenly.
03 - Place the block of feta cheese in the center of the vegetables and drizzle with remaining olive oil.
04 - Roast in the oven for 30 minutes until vegetables soften, caramelize, and feta is golden.
05 - Carefully transfer roasted vegetables and feta to a large saucepan using tongs.
06 - Add vegetable broth to the saucepan and bring to a simmer over medium heat for 5 minutes.
07 - Purée the soup using an immersion blender or standard blender until smooth and creamy. Adjust seasoning as needed.
08 - Ladle soup into bowls, garnish with fresh basil leaves, and serve with crusty bread if desired.