In a large saucepan on medium-high, heat remaining 1 tbsp oil. Add onion, zucchini and carrots and cook, stirring occasionally, until vegetables are soft, about 6 minutes. Add chili paste and continue cooking until flavors blend, stirring frequently, about 2 minutes. Add broth and 2 cups water. Increase heat to high, cover and bring to a boil. Reduce heat to medium and simmer, covered, until vegetables are just tender, 3 to 4 minutes. Add mushrooms and tofu and simmer, covered, until mushroom