Cook green beans in a large pot of boiling, salted water for 3 minutes. Transfer with a slotted spoon to a large bowl of ice water. Allow to cool, drain and pat dry. Transfer to a large serving bowl along with the peanuts. Set aside.
Heat 1 tablespoon olive oil in a skillet over medium and cook shallot and serrano chili, stirring occasionally, until tender, about 3 minutes. Add the ginger paste, lemongrass paste, chopped garlic and cook, stirring, until very fragrant, about 1 minute. Transfer to a small bowl.
Add lime zest, lime juice, sugar, 1/2 teaspoon kosher salt, and remaining 3 tablespoons of olive oil into shallot mixture. Stir to combine.
Pour vinaigrette over warm beans, tossing to coat. Season with kosher salt and fresh black pepper to taste.
Notes
I do prefer using fresh, but, in most markets you can now find chopped garlic, grated lemongrass and ginger paste all made for you in tubes or glass jars. If using fresh, trim the tough outer layers from lemongrass and grate on a Microplane (2 tbsp lemongrass paste).