Make sure you have all your ingredients ready to go. Heat a large wok with a few tbsp of oil on medium high heat. Add the marinated chicken in a single layer, and allow it to cook undisturbed on one side for about 1-2 minutes. It should start to turn opaque, and the bottom will start to turn golden brown.
Stir and continue to fry for a few more minutes until the chicken is no longer pink all over. It will not be cooked through fully but that is ok. We will cook it again later. Remove from pan and set aside.
In the same pan, add 1-2 tbsp more oil, and on medium high heat, add 1 tsp minced garlic, 1 diced onion and 1-2 diced green chilli. Add a pinch of salt and red pepper flakes.
Stir fry for 2-3 minutes until the onions start to turn translucent and everything gets nice and fragrant.
Add 2 tbsp soy sauce, 1 tsp fish sauce, 1 tbsp sweet soy sauce, if using, and 1 tsp brown sugar. Stir, and add about 1/4 cup broth to create your sauce. You can adjust the amount of broth to your liking based on how saucy you want your chicken to be in the end. Stir to combine and bring to a boil.
Add the broccoli florets and bring to a boil.
Add the half-cooked chicken along with a generous handful of thai basil leaves.
Stir and bring to a boil. Simmer in medium for 2-3 minutes until the chicken is cooked through. Give it a taste and add more soy sauce, brown sugar or chilli flakes to taste.
Serve immediately with rice or noodles of choice!