In a Dutch oven, cook pasta according to package directions, adding the beans during the last 5 minutes of cooking.
Meanwhile, combine the cornstarch and broth until smooth; set aside. In a large saucepan, melt butter; add the mustard, basil and garlic powder. Gradually stir in broth mixture. Bring to a boil; cook and stir for 2 minutes or until thickened.
Drain pasta and beans; return to the Dutch oven. Add the mustard sauce and mushrooms; toss to coat. Stir in tomato.