Cook the noodles: Bring a large pot of salted water to a boil.
Cook noodles until just tender. Reserve about 1/2 cup of the starchy cooking water, then drain.
Make the sauce base: In a mixing bowl, combine peanut butter, soy sauce, rice vinegar or lime juice, chili crisp or chili oil, brown sugar or honey, and sesame oil.
Add aromatics: Stir in minced garlic and ginger. Start with a smaller amount of chili oil if you’re sensitive to spice.
Thin the sauce: Whisk in warm water or noodle cooking water, a tablespoon at a time, until the sauce is smooth and pourable.
It should coat a spoon but not feel gluey.
Toss with noodles: Add hot noodles to a large bowl and pour the sauce over. Toss until every strand is glossy. If it feels thick, splash in a bit more cooking water.
Adjust and season: Taste and adjust acidity, salt, and heat.
Add a pinch of salt, extra soy sauce, or a squeeze more lime as needed.
Add toppings: Fold in sliced scallions and any cooked veggies or proteins. Sprinkle with crushed peanuts or sesame seeds for crunch.
Serve: Plate immediately while warm and silky. Finish with an extra drizzle of chili oil if you like it spicy.