Combine broccoli, mushrooms, and carrots in a large glass bowl. Microwave for 5 minutes. Set aside.
Melt the butter in a saucepan. Gradually add-in flour and cook until light brown..
Gently stir-in the milk. Cook while stirring until the texture thickens. Add-in nutmeg and salt. Stir and turn off heat. This is now your bechamel sauce.
Preheat oven to 350 degrees Fahrenheit.
Prepare a wide rectangular baking pan. Start setting-up your masterpiece by spreading the bechamel sauce on the pan. Arrange a layer of lasagna noodles, followed by another layer of vegetables. Sprinkle some mozzarella, Parmesan, and ricotta cheese on top, and then pour-in some bechamel sauce. Create another layer of lasagna noodles. Continue doing the process until you are able to fill your pan. Make sure that the last layer is made-up of lasagna noodles topped with parmesan cheese.
Cover the rectangular pan with aluminum foil. Bake for 25 to 35 minutes.
Remove the foil and bake for another 10 minutes.
Remove from the oven and let cool.
Serve. Share and enjoy!