01 - Preheat oven to 425°F. Line a large baking sheet with parchment paper.
02 - In a bowl, toss zucchini, eggplant, bell peppers, and onion with olive oil, Italian herbs, salt, and pepper. Spread evenly on the prepared baking sheet.
03 - Roast vegetables for 20-25 minutes, stirring halfway, until tender and slightly caramelized. Remove from oven and reduce heat to 375°F.
04 - In a saucepan over medium heat, melt butter. Whisk in flour and cook for 1-2 minutes until bubbling but not browned. Gradually whisk in hot milk, stirring constantly until smooth. Add nutmeg, salt, and white pepper. Simmer for 5-7 minutes, stirring, until thickened. Remove from heat.
05 - Spread a thin layer of béchamel sauce on the bottom of a 9x13-inch baking dish. Top with a layer of lasagna noodles, then half the roasted vegetables, dollops of ricotta, more béchamel, and a sprinkle of mozzarella. Repeat layers, finishing with noodles, remaining béchamel, mozzarella, and Parmesan.
06 - Cover with foil and bake at 375°F for 30 minutes.
07 - Uncover and bake for an additional 15-20 minutes, until golden and bubbling. Rest for 10-15 minutes before slicing. Garnish with fresh basil, if desired.