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 until just done, not soft.
Drain the pasta in a colander, place it in a large bowl, and while still warm, toss with ¾ 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.
