In a large saucepan over medium, heat the vegetable oil. Add the onion and cook, stirring, until golden, about 5 minutes. Add the remaining 11/2 teaspoons cumin and cook, stirring, for another minute.
Add the potatoes, corn and chicken broth, bring to a boil and simmer for 15 minutes, or until the potato is tender. Transfer 11/2 cups of the mixture (mostly solids) to a blender and carefully blend until smooth. Return the mixture to the saucepan, add the chicken and salsa, and cook until just heated through. Add salt and lime juice, to taste, and water, if necessary, to achieve the desired consistency.
Divide between 4 serving bowls and garnish each portion with some of the tortilla strips and cilantro, if desired.
Nutrition information per serving: 400 calories; 110 calories from fat (28 percent of total calories); 12 g fat (2 g saturated, 0 g trans fats); 85 mg cholesterol; 39 g carbohydrate; 4 g fiber; 10 g sugar; 34 g protein; 1,140 mg sodium.