In a large pot over medium heat, warm the avocado oil. Add the onion and sauté for 3-5 minutes until soft and translucent. Add the ginger and red curry paste and stir to combine.
Add the carrot, red pepper and butternut squash, salting the vegetables with about 1 teaspoon kosher salt, and stir to combine. Add the chicken, if using, and stir.
Stir in the coconut milk, chicken stock and fish sauce. Stir to combine. Let simmer on low heat until vegetables are soft and chicken is cooked, about 15-20 minutes.
Add the lime juice and taste for seasoning, adding more salt if necessary.
Serve with steamed rice or cauliflower rice and optional garnish.