Heat the avocado oil in a large pot or Dutch oven over medium heat.
Add the diced yellow onion and cook 3 to 4 minutes, stirring occasionally, until it begins to soften.
Stir in the curry paste (or curry powder), minced garlic, and grated ginger; cook 1 to 2 minutes until fragrant.
Add the chopped carrots and red bell pepper, cover, and cook 3 to 4 minutes until they begin to soften.
Stir in the chopped chicken and chopped zucchini.
Pour in the coconut milk, chicken broth, maple syrup (or sugar), fish sauce (if using), and sea salt; bring to a full boil.
Reduce heat to medium and simmer, stirring occasionally, for about 20 minutes until the chicken is cooked through and vegetables are tender.
Stir in the Thai basil just before serving, then ladle into bowls and enjoy.