Bring a large quantity of water to a boil in a stockpot.
To make the sauce, heat the olive oil in a medium-size saucepan over medium heat. Add the garlic and crushed red pepper flakes, and cook 30 seconds. Stir in the mushrooms and cook until brown and juicy, about 10 minutes. Mix in the tomatoes, rosemary, and salt, and cook, stirring often, for 10 minutes. If the sauce begins to splatter during cooking, lower the heat to medium-low. Keep the sauce warm while cooking the linguine.
Drop the linguine into the boiling water and cook until al dente. Taste one along the way to avoid overcooking it. Drain thoroughly in a colander and return to the pot. Pour on the sauce and toss. Serve with a light sprinkling of Parmesan cheese.
Recipe courtesy of Jeanne Lemlin's VEGETARIAN CLASSICS (HarperCollins, 2001)