Preheat the oven to 375°F and lightly grease or spray a 9x13-inch baking dish.

Bring a large pot of salted water to a boil. Cook the pasta until just shy of al dente, about 2-3 minutes less than package directions. Drain and set aside.

Heat a large skillet over medium high heat. Add the olive oil, onion, bell pepper and ¼ teaspoon of the salt. Cook, stirring frequently until softened, about 3-4 minutes.

Add the sausage and cook for 5-6 minutes, breaking it into small crumbles, until well browned and no pink remains.

Add the garlic, Italian seasoning, and black pepper, and cook for 1 minute until fragrant.

Reduce the heat to medium-low. Add the marinara sauce and simmer for 2-4 minutes until the sauce is heated through. Remove from the heat.

In a medium bowl, stir together the ricotta, egg, ½ cup of the Parmesan, and ¼ teaspoon of salt until smooth.

In the same pot the pasta cooked in, toss the cooked pasta with about 1 cup of the marinara sauce until evenly coated.

Spoon half the pasta into the prepared baking dish, dollop and gently spread half the ricotta mixture over the top, then add 1 cup of the marinara sauce, and then ½ cup of the mozzarella.

Repeat the layers with the remaining pasta, ricotta, and sauce. Finish with ½ cup mozzarella and the remaining ¼ cup of Parmesan.

Cover loosely with foil and bake for 20 minutes. Remove the foil and bake for 10-15 minutes more, until the cheese is golden and bubbling at the edges. Let rest for 5 minutes before serving.