Heat oil in a large saucepan over medium heat. Add green onions and saute about 3 minutes or until tender. Add 3 cups broth; bring to boiling. Add cauliflowerets; return to boiling. Reduce heat to medium-low; cook about 6 minutes or until cauliflower is almost tender.
Whisk together flour and remaining 1 cup chicken broth in a small bowl. Stir into saucepan. Bring to boiling; cook, stirring occasionally, 2-3 minutes or until soup is thickened.
Remove soup from heat. Add cheese, stirring until melted. Stir in roasted red peppers, salt if using and hot-pepper sauce, breaking up red peppers with a wooden spoon.