Preheat oven to 350 degrees F. Lightly grease a 3-quart rectangular baking dish; set aside. Cook lasagna noodles according to package directions; drain and set aside.
In a large skillet cook meat over medium heat until browned, using a wooden spoon to break up meat as it cooks. Add mushrooms; cook about 3 minutes more or until softened. Drain well. Remove from heat. Stir marinara sauce into meat mixture. Set aside.
Spread 1 cup of the meat mixture into the bottom of the prepared baking dish. Top with three of the cooked noodles. Cover noodles with half of the ricotta cheese mixture and another 1 cup of the meat mixture. Repeat layers once. Top with the remaining three noodles. Spoon the remaining meat mixture over. Sprinkle with mozzarella cheese.
Bake, covered, for 45 to 50 minutes or until hot and bubbly. Uncover. Bake for 5 minutes more.