Cook pasta according to package directions. If serving cold, rinse under cold water after draining and toss with a little sesame oil.
Make the sauce: whisk together peanut butter, soy sauce, honey, sesame oil, garlic, lime juice, and a splash of warm water. Whisk until completely smooth and pourable. Taste — adjust with more soy sauce for salt, honey for sweetness, or lime for brightness.
Toss noodles with sauce until every strand is coated. Add more water a tablespoon at a time if too thick.
Serve topped with chopped green onions, sesame seeds, or sliced cucumber if you have them.