Preheat oven to 350°.
Lightly grease baking dish.
Cook grits according to instructions on box; set aside.
Crumble sausage in a large skillet; add onion.
Cook over medium heat until meat is browned, stirring occasionally.
Combine grits, sausage mixture, salsa, and half of the cheese.
Spoon into baking pan.
Bake for 15 minutes.
Sprinkle with remaining cheese, and bake an additional 5-10 minutes, or until cheese melts.