Serves 4 to 6.
Place the butter and flour in a small saucepan and cook over medium heat, stirring frequently, for 3 minutes, or until bubbly. Add 1/2 cup of the milk and stir until smooth. Add the remaining 1 cup of milk and cook for 7 to 8 minutes, or until it begins to boil. Remove from the heat and stir in the Parmesan. Season to taste with salt and pepper.
Meanwhile, place the red bell peppers directly on the stove burner (or under a broiler if you have an electric stove) and cook over high heat, turning occasionally, for 15 minutes, or until the peppers are almost completely black on the outside. Place the blackened peppers in a small bowl and cover tightly with plastic wrap. Let stand for 10 minutes to loosen the skin. Peel the skin off and cut the peppers in half. Discard the seeds and cut each half into 2 or 3 strips.
Stem the zucchini and cut it lengthwise into 1/8 inch thick slices.
Cut the top and bottom off the tomato and discard them. Cut the remaining tomato into four even slices.
Cut the mushrooms into 1/4 inch thick slices.
Preheat the oven to 350°F.
Spoon 1/2 cup of the sauce into the bottom of an 8 inch square baking pan. Cover the sauce with a layer of noodles. Arrange the zucchini slices over the noodles and spread with 3/4 cup of the ricotta. Place the roasted bell peppers over the ricotta and spread with 1/2 cup of the sauce. Form another layer of noodles and top with the mushrooms. Spread the remaining 3/4 cup of ricotta over the mushrooms and top with the remaining sauce. Place the tomato slices over the sauce and cover with aluminum foil. (At this point the lasagna can be refrigerated for up to 1 day).
Bake the lasagna covered for 40 minutes. Remove the foil and sprinkle the top with the mozzarella. Bake for 10 to 15 minutes uncovered, or until the cheese is lightly browned. Remove the lasagna from the oven and let it stand for 10 minutes before serving.