Preheat your oven to 375°F (190°C). Lightly grease a 9x13 inch baking dish. Pour about half of the marinara sauce into the bottom of the prepared dish, spreading it evenly.

Wash and trim the ends of the zucchini. Using a mandoline slicer or a very sharp knife, slice the zucchini lengthwise into thin strips, about ⅛ to ¼ inch thick. Lay the slices on paper towels, sprinkle lightly with salt, and let sit for 10 minutes to draw out excess moisture. Gently blot dry.

Heat a grill pan or large skillet over medium-high heat. Lightly brush the zucchini slices with olive oil and season with a pinch of salt and pepper. Grill or sauté for 1-2 minutes per side until slightly tender and pliable with grill marks. Set aside to cool.

In a large mixing bowl, combine the egg, ricotta cheese, Pecorino Romano, chopped fresh basil, and minced garlic. Season with ½ tsp salt and ¼ tsp black pepper. Mix thoroughly until smooth and well combined.

Lay a grilled zucchini strip flat on a clean surface. Spoon about 1-2 tablespoons of the ricotta filling onto one end of the strip. Carefully roll the zucchini tightly from the filled end to the other, creating a small roll.

Place the rolled zucchini rollatini seam-side down in the prepared baking dish over the marinara sauce. Arrange them in a single layer. Repeat with remaining zucchini strips and ricotta filling.

Pour the remaining marinara sauce over the top of the rolls. Sprinkle evenly with the shredded mozzarella cheese.

Bake for 20 minutes, or until the cheese is melted, bubbly, and lightly golden brown, and the zucchini is tender. For a more golden top, briefly place under the broiler for 1-2 minutes, watching carefully. Garnish with fresh basil leaves and serve immediately.