Preheat the oven to 400℉.
In a small saucepan, boil the peas in salted water for 5 minutes. Drain the cooked peas and set them aside.
In a medium saucepan, melt the butter over medium-low heat. Whisk in the gluten free flour until completely combined. Cook for 2 minutes, until the flour and butter mixture is bubbling, stirring constantly.
Slowly pour in the milk, whisking constantly to avoid lumps forming. Bring the sauce to a boil, then reduce it to a simmer. Once the sauce has thickened, season the béchamel with 1½ teaspoons of salt, fresh black pepper, and a bit of freshly grated nutmeg. Remove the sauce from the heat.
In a large mixing bowl, mix together the ricotta, cooked peas, lemon zest, 1/2 teaspoon of salt, fresh pepper, and garlic. Use an immersion blender to roughly blend the mixture together. It is ok if there are some remaining chunks of peas.
Assemble the lasagna in an 8 x 10-inch casserole dish. Spread 1/2 a cup of the béchamel sauce in a thin layer over the bottom of the dish. Layer three lasagna noodles over the sauce to cover the base of the pan. It is ok if the noodles overlap slightly. Scoop half of the ricotta filling over the noodles, followed by a layer of zucchini, 1 cup of shredded mozzarella, and 1 cup of béchamel sauce. Repeat for a second layer, finishing with a layer of lasagna noodles, the remaining béchamel, and mozzarella.
Bake the lasagna uncovered for 30 minutes, rotating the pan halfway through. The lasagna is finished when the top is golden brown and bubbling at the edges. Remove the lasagna from the oven, tent the top with foil, then allow it to rest for 15 minutes before slicing.
Slice and serve the lasagna with a side salad of your choosing. Leftover lasagna will keep in a container in the fridge for up to 5 days.