Heat oil in a large heavy saucepan over low heat. Add onions and cook, stirring, for 5 minutes. Add celery, bell pepper, garlic and cumin; cook, stirring, for 2 to 3 minutes. Add broth, thyme and bay leaf and bring to a boil. Reduce heat to low and simmer, uncovered, for 10 minutes.
Add corn and potatoes, return to a simmer and cook until all the vegetables are tender, 5 to 10 minutes. Place cornstarch in a small bowl, slowly add evaporated milk, stirring until smooth. Stir into the soup and return to a simmer. Cook, stirring, until thickened, about 2 minutes. Discard the bay leaf. Season with salt, pepper and cayenne.
Per serving: 200 calories; 2 g fat (1 g sat, 1 g mono); 5 mg cholesterol; 38 g carbohydrates; 0 g added sugars; 10 g protein; 4 g fiber; 208 mg sodium; 608 mg potassium.
Nutrition Bonus: Vitamin A (20% daily value), Vitamin C (64% dv), Potassium (17% dv), Calcium (19% dv).