Supplementing peanut butter with silken tofu lowers fat and boosts nutrition in this spicy dressing. Whole wheat pasta provides another nutritional upgrade, and its nutty flavor complements the peanut sauce.
Bring large pot of lightly salted water to a boil.
Make dressing: In blender or food processor, combine all dressing ingredients; process until smooth and creamy, stopping once or twice to scrape down sides of work bowl. Set aside. (Dressing can be made up to 2 days ahead and refrigerated.)
Drop spaghetti into boiling water and stir to prevent sticking. Cook until just tender, 8 to 10 minutes. Drain and rinse with cold running water. Drain again, shaking colander. Transfer spaghetti to large bowl, drizzle with oil and toss to coat.
Add carrots and bell pepper to spaghetti in bowl. Add reserved dressing and toss to coat. Transfer to large shallow serving bowl. Sprinkle with cucumber, cilantro, scallions and peanuts. Garnish with lime wedges and serve.