Heat a tablespoon of olive oil in a 12 inch skillet over medium high heat. Add the sausage and onions and cook until the onions soften and the sausage begins to brown. About 6 minutes. Add the garlic and cook another 2 minutes until fragrant.
Stir in the chicken broth, rotel tomatoes, and half and half. Add the pasta. Bring to a boil, cover and simmer for about 15 minutes until pasta is tender the liquid is mostly absorbed.
Top with cheese and scallions. Broil for about 3-4 minutes until the cheese develops nice golden spots. Serve.