Roast the peppers (can do 2-3 days ahead): Preheat your toaster oven to Broil and line the baking tray with foil. Place the bell peppers on the tray and roast, turning occasionally with tongs, until blackened in places, 30-40 minutes. Transfer the peppers to a large bowl and cover with plastic wrap. Let steam for 10 minutes. Uncover and let cool. With a paring knife, remove the skin, stems, and seeds. Finely chop peppers.

In a large nonstick saucepan or Dutch oven, heat oil over medium-high heat. Add onion, cauliflower, and garlic and cook, stirring, until vegetables are lightly browned, about 7 minutes. Add broth or stock and evaporated milk; cover and bring to a boil. Reduce heat and simmer, covered, until vegetables are tender, 8-10 minutes.

Carefully transfer to a food processor or blender. Add half of the reserved roasted peppers (about one cup) and puree until smooth. Return to the pot and add the remaining roasted peppers; bring to a simmer. Remove from the heat and stir in 6 tablespoons of the cheese and 2 tablespoons of the green onions, stirring just until cheese melts.

Ladle into 6 serving bowls. Sprinkle each serving with 1 tablespoon each of the remaining cheese and green onions.