How to Make It
Combine the broth, chicken, squash, sweet potato, ginger, lime zest, and lemongrass (if desired) in a large pot and bring to a boil. Reduce heat and gently simmer until an instant-read thermometer inserted in the thickest breast registers 165° F and the vegetables are tender, 18 to 22 minutes.
Transfer the chicken to a plate and let rest for 5 minutes.
Using 2 forks, shred the chicken into large pieces.
Add the coconut milk, fish sauce, and shredded chicken to the pot. Cook until warm, 3 to 5 minutes. Discard the lemongrass.
Serve topped with the chili oil and cilantro and with the lime wedges on the side.