Heat oven to 375°F. Lightly grease a 9x13-inch baking dish.
Boil rigatoni in salted water until very al dente, about 2 minutes shy of package time. Reserve 1/2 cup pasta water and drain.
Warm olive oil in a large skillet over medium heat. Brown the sausage, breaking it up, 6 to 8 minutes. Drain excess fat.
Stir in onion and cook until translucent, 4 to 5 minutes. Add garlic and cook 30 seconds.
Mix in tomato paste and cook 1 minute. Pour in marinara and the reserved pasta water. Season with oregano, red pepper flakes, 1 tsp salt, and black pepper. Simmer 5 to 8 minutes, then stir in half the basil.
In a bowl, combine ricotta, 1 cup mozzarella, and 0.25 cup Parmesan with a pinch of salt and pepper.
Toss the drained rigatoni with the sausage sauce until evenly coated.
Spread a thin layer of sauce in the baking dish. Add half the pasta, dot with half the ricotta mixture, and sprinkle with 1 cup mozzarella and 0.25 cup Parmesan.
Repeat with remaining pasta and ricotta. Top with the rest of the mozzarella and Parmesan.
Cover with foil and bake 15 minutes. Uncover and bake 10 to 12 minutes more until bubbly and lightly browned. Rest 10 minutes, then garnish with remaining basil.
Notes
Variation: Swap half the sausage for cremini mushrooms, or fold in a couple handfuls of baby spinach with the sauce. Make-ahead: Assemble up to 1 day in advance; cover and refrigerate, then add 5 to 10 minutes to the bake time. Leftovers freeze well for up to 2 months; reheat covered at 350°F until hot.This recipe is an original creation inspired by classic Easy Rigatoni al Forno Recipe flavors. All ingredient ratios and instructions are independently developed.