Heat the olive oil in a large pot over medium heat. Once hot, add the onion and salt. Sweat the onion until soft, about 4-5 minutes, before adding the curry paste.
Stir the paste and onion together and cook until fragrant, about 30 seconds, before adding the powdered peanut butter, coconut milk, and chicken broth. (Optional: Add a handful of chopped cilantro.)
Bring to a simmer before adding the ramen and chopped rotisserie chicken. (If you're not in a hurry, you can cover and simmer for longer before adding the chicken and ramen to further develop flavors.)
Cook for 4-5 minutes until the chicken is heated through and the ramen softens and separates.
Add the fish sauce, a squeeze of lime juice, and salt to taste before serving.
Garnish with fresh cilantro and minced shallots or red onion, lime wedges, chili crisp, and wonton strips or fried noodles, if desired.