1Heat oven to 350º. Cook spaghetti in 4-quart Dutch oven as directed on package; add frozen vegetables for the last 5 minutes of cooking. Rinse with cold water; drain.
2Heat oil in Dutch oven over medium-high heat. Cook mushrooms in oil about 3 minutes, stirring occasionally, until crisp-tender. Stir in flour, basil, salt, nutmeg and pepper. Cook over medium heat, stirring constantly, until mixture is smooth and bubbly; remove from heat. Gradually stir in milk. Heat to boiling, stirring constantly. Boil and stir 1 minute.
3Stir in spaghetti-vegetable mixture, tofu and 1/2 cup of the cheese. Spread in ungreased 2-quart casserole. Sprinkle with remaining cheese.
4Bake uncovered 25 to 30 minutes or until hot and bubbly.