Preheat oven to 350 degrees F. Lightly grease 3-quart rectangular baking dish; set aside. Cook pasta according to package directions. Drain; set aside.
Meanwhile, in large skillet cook sausage and onion until meat is browned and onion is tender. Drain fat, Return sausage and onion to skillet. Stir in green salsa.
In prepared baking dish layer half of the cooked pasta, half the sausage mixture, and half the cheese. Repeat layers. Bake, uncovered, for 35 minutes or until bubbly. Let stand 10 minutes. Top with tomato, jalapeño, and cilantro. If desired, serve with additional salsa. Makes 12 servings.