Heat vegetable oil in a heavy bottom stockpot.
Once shimmering, add scallions, garlic, ginger, and jalapenos. Saute until fragrant, about 2 minutes.
Stir in the bell peppers, mushrooms, and lemongrass. Saute until softened, about 3-5 minutes.
Add chicken broth, coconut milk, fish sauce, curry paste, sugar, salt, lime zest and chicken to the stockpot.
Bring soup to a boil, then cover and continue to cook for 25 minutes. Check chicken to see that it's cooked through fully (no longer pink) before moving on to the next step.
Place cooked chicken on a plate and all it to rest for 10 minutes.
Remove the lid from the soup, and continue to cook at a steady simmer for 10 minutes.
Shred chicken into large pieces and return to the soup.
Taste test the seasoning of the soup and adjust to your liking. (I like to add an additional teaspoon of salt here).
Ladle into bowls, top with freshly chopped cilantro and lime slices, and enjoy!