Start with making the sauce. Heat a large, heavy skillet over medium heat. Add oil to the pan.
When the oil is medium hot, add chopped onion and saute until it is softened approx. 2 minutes. Add minced garlic, saute for 30 seconds. Then add ground beef. Break up large chunks of meat with a spatula and cook until it is no longer pink.
Add bay leaf, fennel, oregano, paprika, chopped basil, and parsley. (Reserve 1 tablespoon each of basil and parsley for ricotta mixture). Stir well. Add Crushed tomatoes, Tomato paste. Mix well and let it cook on medium heat for 5 minutes.
Cover and let the beef mixture cook on low heat for another 15-20 minutes.
While the sauce is simmering, mix ricotta cheese, egg, chopped basil, parsley (reserved while making the sauce), a big pinch of salt, and pepper in a bowl. Set aside.
Using a mandolin - slice zucchini length wise into thin strips. Put the zucchini slices in a bowl. Sprinkle 1 teaspoon of salt, toss gently, and let it rest for 10 minutes.
Drain liquid from the bowl. Place zucchini slices on a clean kitchen towel in single layer. Place another towel on top and press gently to soak all the remaining liquids. Repeat with remaining Zucchini slices.
Preheat oven to 375 F degrees. Prepare an 8 x 8-inch deep baking dish.
Assembling the lasagna
Spread a thin layer of beef sauce at the bottom. Arrange zucchini slices in a single layer, slightly overlapping each other.
Spoon ricotta mixture over the zucchini slices, spread to a thin layer. Top the ricotta layer with another layer of zucchini slices. Then top it with beef sauce followed by mozzarella cheese.
Repeat the above two steps for two more times until you have used all the zucchini slices. At the end, on the top layer sprinkle mozzarella cheese and Parmesan cheese.
Cover the baking dish loosely with an aluminium foil. Bake for 30 minutes in the preheated oven at 375 F degrees.
Carefully remove the foil and bake for 15 minutes more until the cheese is bubbly and small brown spots starts appearing.
Remove from the oven and let it rest for at least 20 minutes before serving.