Soak the noodles. Place the 12 lasagna noodles in a 9x13 baking dish in a single layer. Pour hot tap water over them until they're fully submerged, add the tablespoon of olive oil, and let them soak for 20 minutes. After the first 3–4 minutes, gently separate any noodles that have started to fuse—run a butter knife or your fingers between them to keep them from sticking as they soften. Stir once more halfway through. They should be pliable but still firm after 20 minutes. Drain and lay them flat on a clean kitchen towel.

Preheat the oven. Preheat to 375°F. Coat a separate 9x13 baking dish with cooking spray.

Make the meat sauce. Heat the olive oil in a large skillet over medium heat. Add the diced onion, kosher salt, Italian seasoning, black pepper, and crushed fennel seed. Cook for 4–5 minutes, until the onion is tender and starting to brown. Add the minced garlic and cook for 30 seconds, until fragrant. Add the ground beef and cook for 5–7 minutes, breaking it apart with a wooden spoon, until browned and cooked through. Pour in the marinara sauce and the crushed red pepper flakes if using. Stir to combine, then remove from the heat.

Make the ricotta filling. In a large bowl, stir together the ricotta, cream cheese, egg, and kosher salt until smooth and fully combined. Fold in the chopped spinach, ½ cup of mozzarella, and ½ cup of Parmesan.

Spread the base. Spread 1½ cups of the meat sauce evenly across the bottom of the prepared baking dish.

Assemble the rolls. Lay one soaked noodle flat on a clean work surface. Spread about 3 tablespoons of the ricotta mixture along the noodle. Spoon 1 tablespoon of the meat sauce over the ricotta. Starting at one short end, roll the noodle up tightly. Place it seam-side down in the baking dish. Repeat with the remaining noodles.

Top the rolls. Spoon the remaining meat sauce evenly over the rolls. Sprinkle with the remaining 1 cup of mozzarella and ½ cup of Parmesan.

Bake. Cover the dish tightly with foil and bake for 15 minutes. Uncover and bake for another 10–15 minutes, until the sauce bubbles around the edges and the cheese begins to brown.

Broil for the finish. If your baking dish is broiler-safe, turn the oven to broil and broil for 1–2 minutes, until the cheese is browned in spots. Watch it the entire time—it goes from golden to burnt fast.

Rest and serve. Let the dish rest for 5 minutes before serving. Garnish with fresh basil or parsley.