Begin by cooking the rice noodles according to the package instructions. Typically, this involves boiling them in salted water until tender. Drain and set aside.
In a large pot, heat the avocado oil over medium heat. Add the finely chopped onion and sauté until translucent, about 3-4 minutes. Stir in the minced garlic and cook for another minute until fragrant.
Add the chopped chicken breasts to the pot. Cook until the chicken is browned and cooked through, about 5-7 minutes, stirring occasionally.
Pour in the full-fat coconut milk and add the green curry paste. Stir well to combine, making sure the curry paste is evenly distributed throughout the soup.
Next, add the chopped broccoli, carrots, red bell pepper, and zucchini to the pot. Stir to mix everything together and allow the soup to simmer for about 10 minutes, or until the vegetables are tender.
If desired, add fish sauce and red pepper flakes to taste. Adjust the seasoning according to your preference. Finally, gently fold in the cooked rice noodles, allowing them to heat through. Serve hot, garnished with fresh herbs or lime wedges if desired.