Baked Spaghetti

Preheat oven to 350℉. Coat a 9-by-13-inch baking dish with cooking spray. Bring a large pot of water to a boil.

Cook spaghetti according to package directions until al dente; drain and transfer to a large bowl; let cool slightly, about 10 minutes. 

Meanwhile, heat 1 tablespoon oil in a large nonstick skillet over medium heat. Add ground beef; cook, stirring and breaking up the beef with a wooden spoon, until no longer pink, about 6 minutes. Stir in Italian seasoning, salt, crushed red pepper and pepper; cook, undisturbed, until fragrant, about 1 minute. Use a slotted spoon to transfer the mixture to a medium bowl. (Do not wipe the pan.) 

Add the remaining 1 tablespoon oil to the pan and heat over medium heat. Add onion; cook, stirring occasionally, until soft and translucent, about 2 minutes. Add mushrooms and garlic; cook, stirring occasionally, until fragrant, about 5 minutes. Add spinach; cook, tossing often with tongs, until wilted, about 2 minutes. Stir in marinara sauce and the reserved ground beef mixture. Bring to a simmer over medium heat; simmer, undisturbed, until slightly reduced, about 5 minutes. 

Whisk eggs, ricotta and 1/4 cup each mozzarella and Parmesan in a large bowl. Add the spaghetti and toss until coated. 

Stir the marinara mixture into the spaghetti mixture, tossing until completely coated. Transfer to the prepared baking dish and top with the remaining 1/4 cup each mozzarella and Parmesan. Bake until the cheeses are melted and the pasta is warmed through, about 20 minutes. Let stand for 10 minutes. Garnish with basil, if desired.