Place basil, walnuts, garlic, oil, salt, and pepper flakes in food processor. Process, stopping once or twice to scrape down sides, until finely pureed. Transfer pesto to large bowl using spatula.
Bring medium pot of lightly salted water to a boil. Add pasta and cook according to package directions. Drain, reserving 1/2 cup of the cooking water.
Stir 2 or 3 tablespoons of reserved water into pesto. Add pasta and toss, adding more cooking water if necessary for consistency. Divide pasta evenly among 4 plates and sprinkle each serving with tomato and cheese.
Nutritional Info Per Serving.
358 cal, 15 g pro, 42 g carb, 6 g fiber, 16 g fat, 2 g sat fat, 4 mg chol, 249 mg sodium.