Bring a large pot of well-salted water to a boil over high heat. Add the spaghetti and cook according to package directions until the pasta is al dente. Drain in a colander and rinse under cold running water until cool. Transfer the pasta to a large bowl, and toss with 1 tablespoon of the sesame oil.

In a food processor, pulse the garlic until roughly chopped. Add the remaining 5 tablespoons sesame oil, and the peanut butter, soy sauce, vinegar, brown sugar, and 1-1/2 teaspoons salt. Process until smooth, stopping as necessary to scrape down the bowl, about 30 seconds. Set aside.

Trim off any exposed tendon ends from the wide tips of the tenders, if necessary. Season the tenders with 3/4 teaspoon salt and 1/2 teaspoon pepper. Heat the peanut oil in a in a 12-inch nonstick skillet over medium-high heat until hot. Cook the tenders until well browned on both sides and just cooked through, about 3 minutes per side. Transfer the chicken to a cutting board and slice crosswise into 1/2-inch pieces. Add the chicken to the spaghetti along with half of the scallions.

Pour about 1-1/4 cups of the dressing over the pasta and chicken and toss to coat. Add more dressing to taste--you may not need to use it all. Transfer to a serving platter, sprinkle with the remaining scallions, and serve.