Greens and Cheese Vegetable Lasagna

Heat butter in a medium saucepan over medium until foaming. Whisk in flour and cook, whisking constantly, about 1 minute. Add milk 1 cup at a time, whisking to incorporate after each addition. Bring to a simmer and cook, whisking occasionally, until slightly thickened, 6–8 minutes. Remove from heat and add Parmesan, whisking until cheese is melted and sauce is smooth; season béchamel with salt and pepper.

Preheat oven to 350°. Cook lasagna noodles in a large pot of boiling salted water, stirring occasionally, 2 minutes less than package directions; you want them to be very al dente so they won’t become mushy when baked. Drain noodles and transfer to a lightly oiled baking sheet; turn noodles to coat (this will prevent them from sticking to one another and make them easier to handle).

Meanwhile, heat ¼ cup oil in a large skillet over medium-high. Add garlic and cook, stirring constantly, until fragrant, about 1 minute. Add a few handfuls of greens and cook, tossing and adding more greens as they wilt, until all greens are tender, about 5 minutes; season with salt and pepper.

Combine ricotta, eggs, thyme, and lemon zest in a medium bowl; season with salt and pepper.

Lightly oil a 13x9" pan. Arrange noodles to cover bottom of pan, cutting to fit as needed. Spread one-third of ricotta mixture evenly over noodles, then top evenly with one-third of cooked greens. Spoon one-quarter of béchamel over greens, spreading evenly to cover. Add another layer of noodles. Repeat layers 2 more times, starting with noodles and ending with béchamel. Top with a final layer of noodles, then spread with remaining béchamel. Scatter mozzarella over top.

Bake lasagna until bubbling and beginning to brown on top, 45–50 minutes. Let cool at least 20 minutes before serving.