Blend the Cashew Ricotta: Combine the soaked cashews, water, lemon juice, nutritional yeast, garlic, salt, and black pepper in a food processor. Blend until smooth and creamy, stopping to scrape down the sides of the bowl as needed. Once smooth, add the spinach and pulse a few more times until well incorporated.
Preheat the Oven and Prep the Baking Dish: Heat your oven to 400°F. Pour 1 cup of marinara sauce into the bottom of a 9-inch baking dish, spreading it out evenly, and set it aside.
Slice the Zucchini: Remove the ends of the zucchinis and use a mandoline or sharp knife to cut them into thin, lengthwise strips. Aim for a thickness that is thin but sturdy enough to roll. Lightly season both sides of the slices with salt and black pepper.
Grill the Zucchini Strips: Heat a grill pan over medium-high heat and cook the zucchini slices for about 1–2 minutes on each side until softened and grill marks are visible. Transfer the slices to a plate to cool slightly.
Assemble the Rollatini: Lay a zucchini slice flat on a clean surface or cutting board. Spread approximately 1 tablespoon of the cashew ricotta mixture evenly along the slice. Starting at one end, roll the slice tightly into a spiral. Place the rolled zucchini seam-side down in the prepared baking dish. Repeat this process with all the remaining zucchini slices and ricotta.
Bake the Rollatini: Once all the rolls are assembled, pour the remaining marinara sauce evenly over the top. Bake in the preheated oven for 25–30 minutes, or until the rolls are fully warmed through and slightly golden on top. Garnish with fresh basil before serving.