Heat oil in a large saucepan over medium heat. Saut? garlic and scallions until garlic begins to color.
Add broth, tomatoes, corn and spices and bring to a boil. Reduce heat and simmer 5 minutes. Add the chicken and heat until warmed through, about 5 minutes. Add cilantro and lime juice. Stir and warm through. Season to taste with salt and pepper.
Ladle into soup bowls, sprinkle with crumbled tortilla chips and add a dollop of sour cream in the center for garnish.