Cook and drain the ground beef. Reserve 2 tablespoons onions for garnish; stir remaining onions, the soup and salsa into beef. Heat to boiling. Reduce heat to medium-low; cook 5 minutes. Stir in cooked pasta; cook 3 to 5 minutes, stirring occasionally, until thoroughly heated. Sprinkle with cheese; cover and cook just until melted. Sprinkle with reserved 2 tablespoons onions. Prepare green beans. Note: To make ahead, cook the pasta and toss with 1 teaspoon oil in a resealable food-storage plastic bag. Refrigerate until it's time to add it to the skillet.