Boil a large pot of well-salted water and cook noodles 1 minute under the package time. Reserve 1/4 cup of pasta water before draining.
While the noodles cook, whisk together peanut butter, soy sauce, rice vinegar, sesame oil, honey, ginger, and garlic in a large bowl. Add warm water one tablespoon at a time until the sauce flows like a thick dressing.
Drain noodles, toss immediately with 1 teaspoon sesame oil, then pour directly into the sauce bowl. Toss thoroughly with tongs until every strand is coated. Add reserved pasta water if needed to loosen.
Taste and adjust: more rice vinegar if flat, extra soy for depth, chili flakes for heat.
Divide into bowls and top with green onions, crushed peanuts, sesame seeds, and optional chili oil. Serve right away.