Prep: 1. Chop/slice: broccoli, bell peppers, and onion. 2. Mince garlic. Make: 1. In a pot of boiling salted water, cook spaghetti 5 minutes. 2. Add broccoli, bell peppers, and onion; cook until pasta is al dente and vegetables are tender, about 3 minutes more. 3. Reserve 1/2 cup pasta water; drain pasta and vegetables. 4. In a bowl, whisk together peanut butter, sugar, vinegar, soy sauce, oil, garlic, and red-pepper flakes. 5. Add hot pasta and vegetables; toss to coat, thinning sauce with a little pasta water, if necessary. Serve: at room temperature or chilled.