Slice zucchini lengthwise into thin strips. Sprinkle with salt and let sit 15–20 minutes. Pat dry thoroughly.
Preheat oven to 375°F (190°C).
Heat olive oil in a skillet over medium heat.
Cook onion until softened. Add ground beef and cook until browned.
Stir in garlic, marinara sauce, Italian seasoning, salt, and pepper. Simmer 10 minutes.
In a bowl, mix ricotta cheese, egg, and Parmesan cheese until smooth.
Spread a thin layer of meat sauce in a baking dish.
Layer zucchini slices, ricotta mixture, meat sauce, and mozzarella cheese.
Repeat layers until ingredients are used. Finish with mozzarella cheese on top.
Bake uncovered 35–40 minutes until bubbly and golden brown.
Let lasagna rest 10 minutes before slicing.
Garnish with basil or parsley if desired.