Preheat oven to 400. Cut tortillas into 1/2 inch strips. Place on baking sheet. Bake 7-8 minutes or until crisp.
Meanwhile, chop onion. Cut chicken into 1/2 inch pieces. Cook chicken in pot sprayed with vegetable oil, add onion, garlic, chili powder and cumin. Cook and stir. Stir in broth, tomatoes and chilis. Bring to a boil. Reduce heat and simmer.
Snip cilantro. Divide tortilla strips among 4 bowls. Ladle soup over tortillas. Grate cheese over top. Sprinkle with cilantro. Garnish each bowl with lime slice to squeeze juice into soup if desired.