Cook orzo according to package instructions. Set aside.
Heat skillet on medium heat. Add Italian sausage and onions, and cook until sausage is fully cooked, about 8-10 minutes. Add garlic and allow to cook for an additional minute.
Add the cooked orzo, Italian seasoning, heavy cream, marinara sauce, and spinach. Cook for about 3 minutes to heat the ingredients and wilt the spinach.