Preheat the oven to 375.
Start by making the cashew ricotta. Once it resembles ricotta, add the remaining herbed ricotta ingredients and blend until herbs are well incorporated. Set aside until ready to use.
Crumble up the tempeh in a bowl into small pieces. Mix in soy sauce, herbs, spices, and pepper. Heat cooking oil over medium heat in a heavy bottom pan. Add onions and garlic and sauté for 5 minutes, stirring frequently, until onions are fragrant and translucent. Add seasoned tempeh and sauté until tempeh is lightly browned. Remove from heat and set aside.
Cut 1" off each end of the zucchinis. Using a mandoline slicer set at .5mm, slice the zucchini lengthwise to get flat lasagna "noodles".
Layer a 7x11 pan with 1/2 cup of marinara sauce. Top with one layer of zucchini. Add a layer of herbed ricotta, tempeh beef, and marinara sauce in that order. Repeat once more ending with marinara sauce. Add one final layer of zucchini and marinara sauce. Top with vegan parmesan cheese.
Cover in foil and bake for 35 minutes. Uncover and bake an additional 15 minutes until parmesan is golden brown and sauce underneath is bubbling up.
Let sit 10 minutes before serving.
Serving and Storing - Once out of the oven, let the lasagna cool 15 minutes before serving. Serve it with fresh herbs and vegan parmesan alongside artisan bread and a big salad. Store leftover lasagna in an airtight container in the refrigerator for up to 3 days or in the freezer for up to 3 months.
Make in Advance - To make in advance, assemble the lasagna according to the directions. Rather than baking the lasagna, wrap it tightly, and place it in the freezer. Frozen lasagna can be stored in the freezer for up to 3 months. When you are ready to eat it, let it thaw completely in the refrigerator overnight. Then cook it according to the instructions below. It will need a little longer in the oven since it will be chilled.