Heat olive oil in a large skillet over medium-high heat. Add the chicken Italian sausage (casings removed) to the pan and cook until browned (approx. 5 min.) Make sure to crumble the sausage with a wooden spoon so it’s the consistency of ground beef. Drain any fat if necessary.
Stir in onion, chicken broth, pasta sauce, diced tomatoes, Rotel, milk and pasta. Bring to a boil; cover, reduce heat and simmer until the pasta is cooked al dente (approx. 10-12 min).
Add cheese and spinach and cook until cheese is melted (approx. 1 min.).
Serve immediately. Garnish with additional chopped spinach, fresh tomatoes, or mozzarella cheese if desired.