Preheat oven to 400°F (205°C). Cook lasagna noodles in boiling water in a large saucepan until tender but firm, 8 to 10 minutes. Drain, rinse and keep in cold water until ready to use.

In a medium-size saucepan, blend milk, flour and garlic. Cook over medium heat, stirring, until thick. Reduce heat and simmer 2 to 3 minutes.

Remove from heat, add spinach and 2 tablespoons Parmesan cheese.

Spread 2 or 3 tablespoons sauce on bottom of an 8-inch-square baking dish. Place lasagna strips on bottom and trim edges. Spread 2 tablespoons sauce over noodles and add half of spinach mixture with half of mushrooms. Pour 1/4 cup of sauce over mushrooms and sprinkle with half of remaining cheese. Repeat for second layer ending with remaining sauce and cheese.

Bake in preheated oven 30 minutes. Let stand about 10 to 15 minutes to make cutting easier.