Warm the olive oil in a large Dutch oven over medium heat, then add the chopped onion. Let it cook for about 5 minutes until soft and translucent, stirring occasionally so nothing browns too fast. Add the minced garlic and cook for just one more minute until fragrant.
Season the chicken thighs generously with salt and pepper, then place them right into the pot with the onions. Sear for 3 to 4 minutes per side until golden brown on the outside. They don't need to be cooked through yet, since they'll finish simmering in the broth.
Stir in the cumin, oregano, smoked paprika, and chili powder directly into the pot. Let the spices toast for about 30 seconds, stirring constantly so they don't burn. This quick step wakes up their oils and makes the whole chili taste far more layered.
Pour in the pumpkin purée, white beans, chicken stock, minced chipotle pepper, and adobo sauce. Stir everything together until well combined, then bring the pot up to a gentle simmer. Cover and let it cook for 25 to 30 minutes until the chicken is fully cooked through.
Carefully remove the chicken thighs and shred them using two forks on a cutting board or plate. Return the shredded chicken back into the pot and stir in the fresh lime juice. Taste the chili and adjust the salt, pepper, or chipotle to your liking.
Ladle the finished chili into bowls while it's still steaming hot from the pot. Top generously with cilantro, a dollop of sour cream or yogurt, and a handful of crispy tortilla strips. Serve right away so the toppings stay fresh and the chili stays warm.