How to Make It
Preheat the oven to 450°. Heat 2 large nonreactive saucepans. Add 1 tablespoon of the olive oil and the ground turkey to one saucepan; add the sausage to the other. Cook the meats over high heat, stirring to break them up, until cooked through, about 6 minutes. Transfer the meats to a colander. Add 2 tablespoons olive oil to each saucepan, then divide the onions between the pans and cook, stirring, until slightly softened, about 5 minutes. Add half of the garlic to each pan and cook for 1 minute.
Using your hands, crush half of the drained tomatoes into each saucepan, then divide the tomato paste, oregano and crushed red pepper between the pans. Cook the sauce over high heat, stirring, until the tomatoes are softened and the sauce is thickened, about 10 minutes. Combine the 2 pans of sauce; you should have 8 cups. If necessary, stir in enough of the reserved tomato liquid to make 8 cups. Add the cooked meat to the sauce and season with salt and black pepper.
Meanwhile, in a medium bowl, combine the spinach with the ricotta and mozzarella and season well with salt and black pepper.
Spread 1/2 cup of tomato sauce in each of 2 nonreactive 9-by-13-inch baking dishes. Arrange 3 lasagna noodles in each dish and cover each pan of noodles with 1 cup of sauce. Dollop one-quarter of the remaining spinach-cheese filling over the sauce in each pan. Top with another layer of noodles, sauce and the remaining spinach filling and cover with the remaining noodles. Divide the remaining sauce between the 2 pans, spreading it to cover the noodles. Sprinkle each lasagna with 1/2 cup of Parmesan cheese.
Cover the pans with foil and bake the lasagnas for 15 minutes. Remove the foil and bake for about 5 more minutes, or until the lasagnas are bubbling. Let stand for at least 5 minutes before serving.