2 Medium avocados, firm-ripe, peeled, seeded, and sliced
In a large, heavy soup pot, warm the oil over medium heat until it shimmers. Add the onion, and cook, stirring frequently, until tender, 5-10 minutes. Add the garlic, cumin, paprika, and salt, and cook, stirring, for 1 minute. Add the sweet potatoes, stock, chipotle, tomatoes, and beans. Bring the soup to a boil, then reduce the heat to maintain a low simmer and cook, partially covered, until the sweet potatoes are tender but still holding a shape, 20-30 minutes. Stir in the olives. Taste, adding more salt or chipotle if you like.
While the soup simmers, make the tortilla strips: Heat a thin layer of oil in a wide, heavy skillet over medium-high heat. When the oil shimmers, add enough tortilla strips to fit in a single layer and a big pinch of salt. Cook, stirring and tossing occasionally, until golden and crisp, 2-3 minutes. Remove and let drain on paper towels. Repeat with the remaining tortilla strips and oil.
In a small, non-reactive bowl, stir together the diced red onion, lime juice, and a big pinch of salt. Let sit until the soup is ready to serve, at least 5 minutes.
Just before serving, stir in the chicken. Ladle the soup into bowls Garnish with a nest of tortilla strips, avocado slices, queso fresco, cilantro, and olives. Sprinkle with the pickled red onion and drizzle the lime juice over the top.
Extra soup keeps well, refrigerated, for up to 3 days.