Heat the 1 tablespoon oil in a medium (3-quart) saucepan over medium heat. Add the onion and cook, stirring occasionally with a wooden spoon, until softened and just beginning to brown, 3 to 5 minutes. Add the chili powder and tomato paste and cook, stirring, for 15 to 30 seconds; don't let the chili powder scorch. Pour in the broth and scrape the bottom of the pan with the spoon to loosen any cooked-on bits. Add the cilantro sprigs and bring to a boil over medium-high heat. Reduce the heat to medium low and simmer, uncovered, until the broth has reduced by about a third and is very flavorful, 20 to 30 minutes. Discard the cilantro sprigs and season to taste with salt.

While the broth reduces, fry the tortilla strips: Line a plate or tray with two layers of paper towels. Pour 1 inch of vegetable oil into a small, high-sided saucepan (a 6-inch-diameter pan needs about 1-1/2 cups of oil). If you have a candy thermometer, attach it to the pot. Heat the oil over medium heat until it reaches 350 degrees F, or until a tortilla strip sizzles immediately when dipped into the oil. Add 8 to 10 tortilla strips and scrunch them with tongs for a few seconds to give them a wavy shape. Fry until the bubbling subsides and the strips are crisp and very lightly browned, about 1 minute. Transfer to the paper towels to drain, and sprinkle with a little salt while they're still hot. Repeat with the remaining strips.

Divide the turkey, tomato, corn, beans, and tortilla strips between two large soup bowls. If necessary, reheat the broth until it's piping hot. Pour the broth over the ingredients in the bowls. Garnish with the avocado, cheese, cilantro, dollops of sour cream (if using), and big squeezes of lime juice. Serve immediately.