Slice the zucchini lengthwise into thin (about 1/8-inch thick) ribbons using a mandoline, vegetable peeler, or a sharp knife.
Lightly salt the zucchini ribbons and place them in a colander to drain for at least 15-20 minutes. This step is key to drawing out excess moisture and preventing a watery lasagna. Once drained, pat the zucchini thoroughly dry with paper towels.
In a large skillet over medium heat, brown the ground Italian sausage, breaking it up with a spoon as it cooks. Once browned, drain off any excess grease.
Pour in the crushed tomatoes and tomato sauce. Stir in the dried oregano and dried basil. Season with salt and freshly ground black pepper to taste. Bring the sauce to a simmer, then reduce the heat to low and let it cook for at least 15 minutes, stirring occasionally, to allow the flavors to meld beautifully.
In a medium bowl, combine the ricotta cheese, lightly beaten egg, and grated Parmesan cheese. Season with a pinch of salt and pepper. Stir until well combined.
Preheat your oven to 375°F (190°C). Lightly grease a 9x13 inch baking dish.
Spread a thin layer of the tomato sauce on the bottom of the baking dish.
Arrange a layer of zucchini ribbons over the sauce, slightly overlapping to cover the bottom.
Evenly spread about half of the ricotta mixture over the zucchini.
Sprinkle a layer of the cooked sausage over the ricotta, followed by a layer of shredded mozzarella cheese.
Repeat the zucchini, ricotta, sausage, and mozzarella layers.
Finish with a final layer of zucchini, topped generously with the remaining tomato sauce and then a final blanket of mozzarella cheese.
Cover the baking dish tightly with aluminum foil and bake for 30 minutes. Remove the foil and continue baking for an additional 20-25 minutes, or until the cheese is melted, bubbly, and lightly golden brown.
Let the lasagna rest for at least 10-15 minutes after baking before slicing and serving.