Thinly slice sausage and finely chop the onion. Set aside.
Heat olive oil in a large skillet over medium heat. Add the sausage and onion and saute until lightly browned, stirring occasionally. (3-4 minutes).
Add the can of drained and rinsed black beans. Then add the undrained cans of rotel and tomato sauce. Stir in the cup of water, dry pasta, and taco seasoning (or spices*).
Cover skillet and reduce heat to medium low. Let the mixture simmer for 12-15 minutes, stirring occasionally.
When pasta is tender, stir in 3/4 cup of cheese, and top with remaining 1/4 cheese, place lid back on pasta just until cheese melts. Top with chopped green onions.