Heat the olive oil in a large, high-sided, heavy-bottomed skillet over medium heat.
Add the crumbled sausage and cook for about 5 minutes, breaking it apart with a spoon, until fully cooked. Drain any excess grease or liquid and leave the sausage in the skillet.
To the skillet with the cooked sausage, add the uncooked rigatoni, chicken broth, heavy cream, minced garlic, Italian seasoning, and tomato sauce. Stir well to combine.
Bring the mixture to a boil over medium heat. Cover with a lid and cook for 10-15 minutes, stirring frequently to prevent sticking. Cook until the pasta is al dente.
Add the fresh spinach to the skillet and cook on medium heat, stirring frequently, until wilted (about 2 minutes). Alternatively, remove the skillet from heat, cover with a lid, and let the spinach wilt for about 4 minutes using residual heat.
If a thicker sauce is desired, cook the mixture uncovered for a few additional minutes to allow it to reduce.
Remove from heat and season with salt, freshly ground black pepper, and red pepper flakes if desired. Taste before adding salt, as the sausage may already be salty enough.
Stir everything well and serve hot. Enjoy on its own or with garlic bread for a complete meal.