Melt the butter in a saucepan over medium heat. Sprinkle in the flour, while whisking. Once it starts to develop a bit of golden color, stream in the milk, again while whisking. Continue to stir until it is bubbling and thick. Remove from the heat. Season with half of the salt & pepper.
In a skillet over medium-high heat add the spinach or dark leafy greens and a splash of water. Toss in the steam until they are wilted and the liquid is mostly absorbed. Remove and squeeze out any excess liquid and/or place in a wire mesh strainer. They do not need to be dry, just not soggy.
Fold together the ricotta, minced garlic, lemon zest, black pepper and fresh herbs in a separate bowl.
Drizzle about a quarter of the milk sauce into a casserole dish.
Lay down the lasagna noodles*. Spread on the ricotta mixture.
Top with half of the cooked greens, artichoke hearts and fresh peas. Drizzle on more milk sauce.
Top with an even layer of lasagna noodles. Repeat the process.
Finish with noodles, the remaining milk sauce and thinly sliced mozzarella.
Chill at this point or place in an oven preheated to 375.
Bake, covered, for 35-45 minutes until the center is hot. Check by slicing a butter knife in the center. It will feel hot to the touch.
Remove the foil and bake for 5 minutes more until the top is golden.
*I start with dry pasta and lay it uncooked directly in the lasagna. If you prefer a softer lasagna, please feel free to cook the pasta first. Occasionally I use the no-cook lasagna sheets, but not always. Once assembled if it appears dry, simply pour a bit of water (or even broth) in around the edges, just a tablespoon here and there.