Nourishing sweet potato and kale make up the bulk of this perfectly spiced tortilla soup. While you can make it vegetarian, you can also stir in shredded rotisserie chicken for added protein. Serve with your favorite toppings like radishes, avocado, and cilantro. The best part might be the contrast of the soft tortilla strips soaking up the broth and the crispy ones on top.
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.