FOR THE SAUCE:

• Combine the fennel, onion, sage, garlic, fennel seeds, and pepper flakes in food processor and pulse until finely chopped, about 10 pulses; set aside.
• Heat oil in a Dutch oven over medium-high heat until just smoking.
• Add the sausage and cook, breaking up the meat with a potato masher, until the sausage begins to sizzle in its own fat, about 15 minutes.
• Reduce the heat to medium and add the fennel mixture.
• Cook until the vegetables are softened and fragrant, about 4 minutes.
• Add the crushed tomatoes and tomato sauce and bring to a simmer.
• Reduce the heat to medium-low and cook for 5 minutes to allow the flavors to blend.
• Set aside off heat.
• Reserve 2 cups sauce for topping.

FOR THE LASAGNA:

Prepare the noodles:

• Bring 4 quarts of water to a boil in a large pot.
• Add the noodles and 1 tablespoon of salt and cook until just shy of al dente, about 7 minutes.
• Drain the noodles and transfer to a rimmed baking sheet.
• Spray the noodles lightly with oil spray; toss gently to coat (to prevent them from sticking to each other).
• Cut 2 of the noodles in half crosswise.

Prepare the cheese mixture:

• Adjust an oven rack to the middle position and heat the oven to 375 degrees.
• Spray a 13 by 9-inch baking dish with oil spray.
• Combine the mozzarella, provolone, Pecorino, and oregano in a bowl.
• Reserve 2 cups of the mozzarella mixture for topping.

Build the lasagna:

• Lay 3 noodles lengthwise in the prepared dish with the ends touching the short side of the dish, leaving a gap at the far end.
• Lay 1 half noodle crosswise to fill the gap.
• Spread 1½ cups meat sauce over the noodles.
• Dollop ½ cup of the ricotta cheese over the sauce. Use the back of a spoon to spread the ricotta cheese evenly over the sauce.
• Sprinkle with 1 cup of the mozzarella mixture.
• Repeat the layering of noodles, meat sauce, ricotta cheese, and mozzarella mixture 3 more times, switching position of half noodle to opposite end of dish each time.
• Lay the remaining 3 noodles over the top, centered between each end (there is no half noodle for the top layer).
• Spread the reserved 2 cups of sauce over the top layer of noodles, then sprinkle with the reserved 2 cups of mozzarella mixture.

Bake and serve:

• Spray a sheet of aluminum foil with oil spray and cover the lasagna.
• Set the lasagna on a foil-lined rimmed baking sheet.
• Bake for 30 minutes.
• Discard the foil covering the lasagna and continue to bake until the top layer of the lasagna is spotty brown and the lasagna is hot throughout, about 30 minutes longer.
• Let the lasagna cool for 45 minutes. Slice and serve.