Preheat your oven to 375°F (190°C).

In a large skillet, heat the olive oil over medium heat. Add the diced onion and minced garlic, sautéing until the onion is translucent.

Add the ground beef or turkey to the skillet. Cook until browned, breaking it apart with a spoon as it cooks.

Stir in the crushed tomatoes, dried oregano, dried basil, salt, and pepper. Let the mixture simmer for about 10 minutes.

In a mixing bowl, combine the ricotta cheese, egg, a pinch of salt, and pepper. Mix until well incorporated.

In a 9x13 inch baking dish, spread a thin layer of the meat sauce on the bottom.

Layer zucchini slices over the meat sauce, followed by half of the ricotta mixture, and then a third of the mozzarella cheese.

Repeat the layers: meat sauce, zucchini slices, the remaining ricotta mixture, and another third of the mozzarella cheese.

Top with the remaining meat sauce and sprinkle the rest of the mozzarella and Parmesan cheese on top.

Cover the baking dish with aluminum foil and bake in the preheated oven for 25 minutes.

Remove the foil and bake for an additional 15-20 minutes, or until the cheese is bubbly and golden.

Allow the lasagna to cool for about 10 minutes before slicing and serving.