Cook the pasta according to the package directions. Drain and rinse under cold running water. Meanwhile, combine the peanut butter, vinegar, soy sauce, chili-garlic sauce or hot pepper sauce, sesame oil (if using), ginger, lime zest, and salt in a blender. With the motor running, slowly add the canola oil in a steady stream.
Return the pasta to the pot and toss with the dressing. Garnish, if desired, with the cilantro, scallions, and peanuts. Serve immediately or cover and refrigerate for up to 3 hours.
Tip: If you're in the mood for salad rather than pasta, toss the Peanut Butter Dressing with shredded cabbage or lettuce, carrots, and cooked chicken.