Preheat oven to 350 degrees F (175 degrees C). Lightly grease a 9x13 inch baking dish.
Bring a large pot of lightly salted water to a boil. Place pasta in the pot, cook for 8 to 10 minutes, until al dente, and drain.
Heat the oil in a saucepan over medium heat. Stir in the mushrooms, cook 1 minute, and set aside. Melt margarine in the saucepan. Mix in flour, garlic, and basil. Gradually mix in milk until thickened. Stir in 1 cup cheese until melted. Remove saucepan from heat, and mix in cooked pasta, mushrooms, spinach, and soy sauce. Transfer to the prepared baking dish, and top with remaining cheese.
Bake 20 minutes in the preheated oven, until bubbly and lightly brown.