First, prepare the tomato sauce for coating the lasagna rolls: in a saucepan, heat a drizzle of olive oil with the peeled and halved garlic clove. Add the tomato passata, season with salt and pepper, and bring to a boil. Lower the heat, cover with a lid, and simmer until the sauce has reduced and thickened. Remove from the heat and set aside. In another saucepan, place the cleaned and washed spinach leaves with a tiny splash of water and a pinch of salt. Cover and let wilt over low heat.
Drain the spinach, let it cool, and squeeze it thoroughly with your hands to remove as much excess water as possible. Finely chop it with a knife and place it in a bowl with the ricotta, egg, and grated Pecorino. Season with salt, pepper, and a pinch of nutmeg if desired, then stir well to combine.
Cook the lasagna sheets in lightly salted boiling water with a drizzle of olive oil added to prevent sticking, boiling until al dente. Drain, rinse under cold running water to stop the cooking process, and lay them out to dry on a clean kitchen towel. Place the sheets one at a time on a cutting board and spread a generous spoonful of the prepared filling across each one. Spread it evenly using the back of a spoon, then roll up snugly from one end to the other. Cut each rolled cylinder in half with a knife to make 2 roll-ups. Repeat with the remaining ingredients to yield 12 roll-ups in total.
Lightly grease a baking dish with olive oil and coat the bottom with a spoonful of the tomato sauce. Arrange the lasagna roll-ups side by side in two rows. Spoon the remaining tomato sauce over the top and scatter with the well-drained, cubed mozzarella. Bake in a preheated oven at 200°C (400°F) for about 25–30 minutes.
Remove the lasagna rolls from the oven, let them rest for a few minutes to settle, and serve warm.
