Preheat the oven to 375 degrees. Cook the lasagna noodles in a large pot of salted water until just tender, then drain and set aside.

Melt the butter in a saucepan over medium heat. Add the minced garlic and cook for one minute. Stir in the flour and cook for another minute to form a roux.

Slowly whisk in the milk. Continue stirring until the sauce thickens. Season with salt, pepper, and oregano. Remove from heat.

In a skillet, lightly cook the sliced zucchini and mushrooms until softened. Stir in the chopped spinach and cook just until wilted.

Spread a thin layer of white sauce in the bottom of a baking dish. Add a layer of noodles, then half the ricotta, half the vegetables, and more sauce. Repeat the layers once more.

Top with the remaining noodles and sauce. Sprinkle the mozzarella and parmesan evenly over the top.

Bake for 30 minutes until the cheese is melted and the edges are bubbly. Let it rest for 10 minutes before slicing.