1 tablespoon vegetable oil, plus more for frying
2 large onions, chopped
8 cloves garlic, minced
1 tablespoon plus 1 1/2 tsp. coarse kosher salt
1 teaspoon ground cumin
1/2 teaspoon red chile flakes
12 cups reduced-sodium chicken broth
1 can (28 oz.) diced tomatoes
Juice of 2 limes
1 package (8 oz.) small corn tortillas, cut into 1/4-in.-thick strips (see Notes)
2 pounds boneless, skinless chicken breast, cut into 1/4-in.-thick strips
1 cup chopped fresh cilantro
Sliced avocado, sour cream, grated Monterey jack cheese, additional chopped cilantro, and/or sliced green onions for topping