Preheat the oven to 400 degrees. Prepare the veggies: slice the bell pepper in half and remove stems and seeds. Lightly brush the the outside with oil. Gently toss the tomatoes in a bit of oil. Place bell peppers and tomatoes on a baking sheet. Roast for 25 minutes or until tops are golden brown.
While veggies are roasting, heat a large soup pot with 1 tbsp oil. Saute onion for 3-4 minutes, then add garlic and cook another 2 minutes. Toss in the cauliflower.
Pour broth in the pot, and bring to a boil. Reduce heat to a simmer. Simmer for 7-8 minutes. Add the sea salt, and the bell peppers and tomatoes to the pot whenever they are done roasting.
Add fresh basil to the pot. Using an immersion blender or a blender, blend until smooth.
Garnish with fresh basil (optional). Serve hot!