Preheat the oven to 350 F and line a baking sheet with parchment paper.
Place the cauliflower, bell pepper, onion, and garlic on the prepare baking sheet. Bake for 30 minutes, tossing halfway through.
Transfer to a large pot along with the remaining ingredients, holding back some of the cauliflower florets to garnish, if desired. Bring to a boil, then simmer, uncovered, for 5 minutes.
Allow to cool until safe to handle. Puree with an immersion blender or transfer to a countertop blender and blend until completely smooth.