Cook the manicotti pasta according to its directions. Drain and set aside.

In a medium pan, heat the olive oil over medium heat. Once hot, add in the onion and minced garlic. Cook until the onion is transparent, stirring occasionally, about 3-5 minutes. Season with salt and pepper.

Add the ground sausage into the pan. Crumble and cook until no longer pink, about 5-7 minutes. Lightly season with salt and pepper. Remove from heat and let cool completely.

In a medium mixing bowl, combine the spinach, ricotta cheese, sour cream, and mozzarella cheese.

Once the meat mixture is cooled, add into the bowl. Mix until well combined. Season with salt and pepper if needed.

In 11x7 baking dish, pour a thin layer of the tomato sauce just enough to cover the bottom.

Fill each manicotti shell with the filling and place on top of the sauce. Repeat until all the ingredients are used.

Pour the remaining sauce over the filled shells and sprinkle the parmesan cheese on top. Cover the pan with foil and bake for 15 minutes. After 15 minutes, remove the foil and bake for 15 more minutes.