Cook pasta as directed on package. Drain, reserving 1/3 cup of the cooking liquid.
Heat oil in large saucepan over medium heat.
Chop onion and garlic and add to the hot oil; stir in salt and pepper. Cook for 6-8 minutes, stirring frequently.
Chop radicchio and add to onions, along with tomatoes and reserved liquid. Continue to cook for 10 minutes or until warmed through and radicchio is tender and wilted.
Stir in cooked pasta and chopped parsley.
Top each serving with walnuts and fresh Parmesan. Serve with grapes on the side. (Serving size: 1.5-2 cups pasta mixture with 2 tablespoons walnuts and 1 tablespoon cheese; 1/2 cup grapes).