In 12-inch nonstick skillet, heat oil over medium-high heat. Cook onion in oil 3 minutes, stirring frequently, until tender. Add potatoes, chili powder and salt. Cook 5 minutes, stirring frequently, until potatoes are lightly browned. Sprinkle cheese over potato mixture. Cover; remove from heat. Let stand 1 minute or until cheese is melted. Sprinkle with green onions.