Preheat your oven to 375°F. Bring a large pot of salted water to a rolling boil.
Boil the noodles: Cook the lasagna noodles for 2 minutes less than the package instructions say. They should be pliable but still firm. Drain and lay them flat on parchment or a clean kitchen towel. Don’t stack them – they should not touch each other.
Make the filling: In a medium bowl, combine the ricotta, squeezed spinach, egg, minced garlic, oregano, and a generous pinch of salt and pepper. Stir until evenly combined. Taste and adjust seasoning – it should be well-seasoned on its own.
Spread the filling: Lay one lasagna noodle flat. Spoon about 2 heaping tablespoons of the ricotta mixture onto it and spread in an even, thin layer from edge to edge.
Roll them up: Starting at one short end, roll the noodle gently but snugly. Place seam-side down in the baking dish. Repeat with remaining noodles.
Assemble and top: Spread about 1 cup of marinara sauce on the bottom of the dish. Arrange the rolls in a 3x4 or 4x3 grid. Pour the remaining 2 cups of sauce over and around the rolls. Sprinkle the shredded mozzarella evenly on top. Add a pinch of salt and pepper.
Bake: Cover tightly with foil and bake for 20 minutes. Remove foil and bake for another 10 to 15 minutes, until the cheese is melted, golden in spots, and the sauce is bubbling at the edges.
Rest and serve: Let the dish rest for 5 to 10 minutes before serving. This allows the filling to set so the roll-ups hold their shape. Serve with fresh basil or parsley if desired.