How to Make It
Preheat oven to 400°F with an oven rack in upper position.
Heat 2 tablespoons of the oil in a large pot over medium-high. Add onion, and season with ¼ teaspoon of the salt; cook, stirring occasionally, until softened, about 3 minutes. Add chili powder, cumin, coriander, and garlic, and cook, stirring often, until fragrant, about 1 minute. Add tomatoes with juices, and cook, stirring often and breaking up with a spoon, until slightly reduced, 2 to 4 minutes.
Add sweet potato, broth, and water, and bring to a boil. Reduce heat to medium-low, and simmer, partially covered, until potatoes are fork tender, 12 to 15 minutes.
Meanwhile, brush remaining 1 tablespoon oil on both sides of tortillas; season with ¼ teaspoon of the salt. Stack tortillas, and cut into ½-inch strips; place in a single layer on a rimmed baking sheet. Bake in preheated oven on top rack until golden brown, 12 to 15 minutes, tossing halfway through.
Stir kale into soup, and cook, covered, until wilted, 3 to 5 minutes. Stir 2 handfuls of tortilla strips into soup, and, if desired, chicken; cook until soup is heated through, about 2 minutes. Season with remaining ¼ teaspoon salt and several grinds black pepper. Serve with lime wedges, and top with remaining tortilla strips.