In a large pot, bring water to a boil and add the instant noodles seasoning sachet, fish sauce, lemongrass, galangal, kaffir lime leaves, water, chili paste and chilies. Simmer for 2–3 minutes to infuse the flavors.
Using a wire strainer, gently add the shrimp and mushrooms to the soup. Allow them to cook for 2–3 minutes, flipping halfway, or until the shrimp turn pink and opaque.
Remove the shrimp and mushrooms with a strainer and set them aside to prevent overcooking.
Pour evaporated milk into the soup base and add the noodles plus fresh lime juice, stirring well until the noodles are cooked.
Divide the soup into serving bowls, top with the cooked shrimp and mushrooms, and optionally garnish with freshly chopped green onions and/or cilantro. Enjoy!