1. Cook the Noodles: Begin by boiling a large pot of salted water. Add the whole wheat lasagna noodles and cook according to the package directions. Once done, drain and set aside.
2. Prepare the Cauliflower: While the noodles are cooking, chop the head of cauliflower into smaller florets. Rinse thoroughly and set aside.
3. Sauté the Vegetables: In a large skillet, heat the olive oil over medium heat. Add the chopped onion and sauté until translucent, about 5 minutes. Then, add the sliced mushrooms and cook for an additional 4-5 minutes until they are tender. Remove from heat and set aside.
4. Make the Cauliflower Sauce: In a medium saucepan, add the cauliflower florets and cover with water. Bring to a boil and cook until the cauliflower is tender, about 10-12 minutes. Drain and transfer to a blender. Add the low-fat milk, whole wheat flour, onion powder, and a pinch of salt and pepper. Blend until smooth and creamy.
5. Assemble the Lasagna: Preheat your oven to 350°F (175°C). In a greased baking dish, layer the cooked lasagna noodles, followed by a portion of the sautéed mushroom and onion mixture, and then a generous layer of the cauliflower sauce. Repeat the layers, finishing with a layer of cauliflower sauce on top.
6. Add the Cheese: Sprinkle the freshly grated Parmesan cheese over the top layer of sauce. Make sure to distribute it evenly for a beautifully melted, cheesy finish.
7. Bake: Cover the baking dish with foil and bake in the preheated oven for 25 minutes. Remove the foil and bake for an additional 10-15 minutes, or until the top is golden and bubbly.
8. Let It Rest: Once out of the oven, let the Cauliflower Lasagna rest for about 10 minutes before slicing. This will help the layers set and make serving easier.