Preheat oven to 350°F. Cut sausage into ½” cubes. Heat a large non-stick skillet over medium-high heat for 3 minutes. Add sausage and onion; cook 3-4 minutes or until sausage is lightly browned and onion is tender. Stir in ½ cup of enchilada sauce; remove from heat.
Lightly spray a 13 x 9-inch baking pan with non-stick cooking spray. Spread ½ cup of enchilada sauce in bottom of pan. Heat corn tortillas according to package directions; keep warm.
Place approximately ¼ cup sausage mixture on warm tortilla. Top with 1 tablespoon cheese. Roll up enchilada and place seam side down in prepared pan. Repeat with remaining ingredients. Pour remaining enchilada sauce over enchiladas. Sprinkle with remaining cheese.
Cover with foil and bake 25 minutes or until sauce is bubbling and cheese is melted. Let stand 5 minutes before serving. If desired, top each serving with shredded lettuce, chopped tomatoes and sour cream.