Combine coconut milk, chicken broth, fish sauce and lemongrass in a medium saucepan.

Simmer over low heat 10 minutes.  

Add the chicken salt and cayenne to a large bowl. Toss to coat.

Heat a large safe nonstick skillet over medium-high heat. Add half of the oil.

When oil shimmers, add chicken pieces to skillet, in batches, and cook until lightly browned, 4 to 5 minutes, turning halfway through. Transfer to a large Dutch oven and cover to keep warm.

Wipe out skillet.

Add remaining oil to skillet over medium-high heat. Add mushrooms and cook until they begin to soften, 3 minutes. Add garlic and ginger. Cook 1 minute, stirring constantly. Add bok choy and cook 2 to 3 minutes to wilt.

Add vegetables to Dutch oven with chicken. Strain coconut milk mixture into Dutch oven to cover chicken and veggie mixture. Discard lemongrass.

Heat over medium-high heat, stirring gently, until mixture comes to a boil. Stir in the scallions, basil and cilantro.

Remove from heat, ladle into serving bowls and serve.