Casserole might not be the first thing to come to mind when it comes to good eats, but there's a special place in people's hearts for pasta al forno. It's probably all the melted mozzarella and pecorino. How can anything with this much cheese be anything but a home run?
Preheat the oven to 375 degrees.
Remove the sausage from their casings, break up into pieces, and sauté in a skillet until the sausage loses its color.
Bring a large pot of water to a boil over high heat. Add the pasta and cook according to the package directions. Drain and set aside.
Meanwhile, combine the marinara sauce, 1 ½ cups of the mozzarella, peas, ricotta, 6 tablespoons of the pecorino romano, salt, and pepper in a large bowl. Stir in the pasta and sausage, and coat a 2 ½-quart baking dish with cooking spray. Pour the mixture into the baking dish.
In a small bowl, stir together the remaining mozzarella, remaining pecorino romano, and the olive oil. Top the pasta with the mixture. Bake until hot, about 25-30 minutes. Let sit for 10 minutes before serving.