Heat vegetable oil in a large soup pot or wok over high heat.

Season chicken with salt and add to the hot oil, browning all pieces.

Cook the chicken for about 3 minutes, until the outside is browned.

Add sliced mushrooms and toss.

Cook until the mushrooms soften and some moisture evaporates, then reduce heat to medium-low.

Mince the lower portion of the lemongrass stalk and score the upper stalk.

Add the minced lemongrass, grated galangal, chili peppers, and the whites of the green onions to the pot.

Toss until warmed through.

Add the lemongrass stalk, chicken stock, coconut milk, lime juice, fish sauce, brown sugar, and the rest of the green onions (except a few for garnish).

Simmer over low heat for 15 minutes to blend flavors.

Taste and adjust flavors, adding more fish sauce for saltiness, brown sugar for sourness, coconut milk for spiciness, or chilies for heat.

Ladle into soup bowls and garnish with reserved green onion greens, cilantro, and basil.