Fill a large pot with lightly salted water and bring to a rolling boil over high heat. Once the water is boiling, stir in the spaghetti and return to a boil. Cook the pasta uncovered, stirring occasionally, until the pasta has cooked through but is still firm to the bite, about 12 minutes. Drain well in a colander set in the sink.
Melt the peanut butter in a large microwave-safe glass or ceramic bowl, 15 to 20 seconds (depending on your microwave). Whisk the honey, tamari and chilli sauce into the peanut butter, then stir in the sesame oil and ginger. Mix in the garlic and spring onions and toss with the spaghetti. Top with the sesame seeds.