Toss cauliflower, mushrooms, and bell pepper with 2 Tbsp. oil. Sprinkle with thyme and cumin. Toss until evenly coated. Spread in single layer on baking sheet. Roast in preheated 450-degree oven 15 to 20 minutes or until cauliflower is golden brown, stirring occasionally. Meanwhile, heat remaining 2 tsp. oil in large saucepan on medium-high heat. Add onions; cook and stir 5 minutes or until softened. Add vegetable mixture, broth, and pepper. Bring to boil. Reduce heat to low; simmer 10 minutes or until cauliflower is tender, stirring occasionally. Ladle into soup bowls to serve. Makes 8 (1-cup) servings.