In a medium sauce pan, brown the ground beef and season with kosher salt. Drain excess fat when cooked.
Add olive oil to the pan and sauté garlic and onions about 2 minutes. Return the meat to the pan, add crushed tomatoes, basil, salt, and black pepper. Simmer covered on low for 30-40 minutes without adding extra water.
Meanwhile, slice zucchini into 1/8 inch thick slices. Lightly salt and set aside for 10 minutes to release moisture, then blot with paper towels.
Preheat a grill or grill pan to medium-high heat and grill zucchini slices 2 to 3 minutes per side until lightly browned. Place on paper towels to absorb any excess moisture.
Preheat oven to 375°F.
In a medium bowl, combine ricotta cheese, Parmigiano Reggiano, and egg; stir well to mix.
In a 9x12 inch casserole dish, spread 1/2 cup of meat sauce on the bottom. Layer zucchini slices to cover, then spread 1/2 cup ricotta mixture, then sprinkle 1 cup mozzarella cheese. Repeat layering until all ingredients are used, finishing with zucchini and sauce on top. Cover with foil and bake 30 minutes.
Remove foil and bake uncovered for 20 minutes to reduce moisture. Add remaining 1 cup mozzarella on top and bake until melted, about 10 minutes.
Let lasagna stand about 5 to 10 minutes before serving.
Notes
This lasagna is great for meal prep and can be frozen. Adjust seasoning to taste.