Place the garlic and ginger in a food processor fitted with a steel blade. Add the vegetable oil, tahini, peanut butter, soy sauce, sherry, sherry vinegar, honey, chili oil, sesame oil, and ground peppers. Puree the sauce.
Add a splash of oil to a large pot of boiling salted water and cook the spaghetti al dente. Drain the pasta in a colander, place it in a large bowl, and while still warm, toss with 3/4 of the sauce. Add the red and yellow bell peppers and scallions; toss well. Serve warm or at room temperature. The remaining sauce may be added, as needed, to moisten the pasta.
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