Sauté the aromatics. Heat the oil in a large soup pot over medium heat. Add the diced onion and sauté for 4–5 minutes until softened and lightly golden. Add the banana pepper and cook another 2 minutes. Stir in the fire-roasted tomatoes and garlic, and cook for about 5 minutes, stirring occasionally, until the mixture reduces slightly and smells rich and sweet.
Build the broth. Stir in the toasted cumin, oregano, whole cloves, bay leaf, and a generous pinch of salt. Pour in the chicken stock, scraping up any browned bits from the pot. Bring to a gentle simmer and cook uncovered for 10–15 minutes to let the flavors meld.
Add the chicken. Stir in the shredded chicken and simmer for 5 more minutes, just to warm through. Remove and discard the bay leaf and cloves.
Finish with citrus. Remove from heat and stir in the lime and orange juice. Taste and season with additional salt as needed — the broth should taste bright and balanced.
Serve. Place a handful of fried tortilla strips in each bowl. Ladle the soup over top, then garnish with lime slices, cilantro, and diced avocado if desired. Serve immediately.