Marinate the Chicken and Shrimp:
In a large bowl, combine the chicken with 1 tablespoon fish sauce, 1 tablespoon sugar, 1 tablespoon turmeric powder, and a pinch of salt and pepper. Mix well and let it marinate for about 30 minutes.
In a separate bowl, marinate the shrimp with 1 tablespoon fish sauce, 1 teaspoon sugar, and a pinch of turmeric powder. Set aside for 15 minutes.
Cook the Broth:
In a large pot, heat 2 tablespoons of vegetable oil over medium heat. Add the halved onion and minced garlic, sauté until fragrant.
Add the marinated chicken and cook until slightly browned on all sides.
Pour in the chicken broth or water and bring it to a boil. Skim off any impurities that rise to the surface.
Reduce the heat to a simmer, add the pork belly slices (if using), and cook for about 30 minutes until the chicken is tender.
Season with the remaining fish sauce, sugar, and a pinch of salt and pepper. Adjust to taste.
Cook the Shrimp:
In a small pan, heat a little oil over medium heat. Add the marinated shrimp and cook for 3-4 minutes until pink and cooked through. Set aside.