In large saucepan, heat oil over medium heat; sauté onion, garlic, zucchini, chili powder, salt and pepper, stirring occasionally, until onion is softened, about 5 minutes.
Add 3 cups of hot water, tomatoes and beans; bring to boil. Reduce heat, cover and simmer for 15 minutes.
Meanwhile, cut tortilla into thin strips. In large skillet, toast tortilla strips over medium-low heat, stirring often, until crisp and golden, about 8 minutes.
Ladle soup into bowls. Garnish with tortilla strips and coriander.