Cook spaghetti according to package instructions (but without oil). Drain and refresh with cool water; set aside.
Meanwhile, coat a large nonstick skillet with cooking spray and set over medium heat. Add onion and vegetables; sauté until softened, about 3 minutes. Add curry powder; cook 20 seconds more. (Note: You can use any frozen vegetable mixture in this dish such as Chinese vegetables, or even just plain broccoli.)
Pour in broth and bring to a simmer, scraping up any browned bits on bottom of skillet with a wooden spoon; cook 1 minute. Stir in yogurt; bring mixture to lowest possible simmer. Stir in spaghetti, cilantro and scallions; serve at once. Yields about 1 heaping cup per serving.