Heat oven to 400° F (205° C).
Heat oil in a large pan over medium heat. Add onion and sauté for 4-5 minutes to soften. Add garlic and cook a minute longer.
Add ground turkey and cook, breaking into small pieces with a wooden spoon while cooking.
Season turkey with salt, pepper, oregano, and half of the basil (if using fresh basil, wait and add during last 10 minutes of sauce simmer time).
Pour crushed tomatoes and tomato sauce into turkey, add bay leaf, and bring to a low simmer. Reduce heat and simmer for 30 minutes, stirring occasionally.
While sauce is simmering, cut ends off of each zucchini and use a mandolin slicer to slice zucchini into 1/8" thick slices.
Spray a baking sheet with cooking spray. Lay zucchini slices out in a single layer. Spray top side lightly with cooking spray and season lightly with salt and pepper. Place baking sheet in oven and roast for 15-20 minutes. When removing from oven, dab zucchini slices with a paper towel or clean kitchen towel if they appear watery.
While sauce simmers and zucchini bakes, mix ricotta, egg, half of parmesan, and nutmeg in a small bowl.
When sauce and zucchini slices are ready, remove bay leaves from sauce and ladle 1/3 of the sauce into the bottom of a 9x11" baking dish. Add layer of zucchini on top of sauce. Spread 1/2 of the ricotta mixture on top of zucchini slices. Sprinkle with 1/2 cup of mozzarella.
Repeat next layer with half of the remaining sauce, remaining ricotta, zucchini, and 1/2 cup of mozzarella. Top with remaining sauce, then mozzarella and parmesan.
Bake for 30 minutes until sauce is bubbling and cheese is melted. Let stand for about 10 minutes before serving.