Heat 2-quart nonstick saucepan over medium-high heat. Add ground beef and onions; cook 4 to 6 minutes, stirring frequently, until beef is thoroughly cooked and onions are tender.
Stir in tomatoes, broth, chili powder and ketchup. Heat to boiling. Reduce heat to medium-low; cover and simmer 5 minutes. Increase heat to medium. Uncover; cook 5 minutes longer.
Stir in tortilla strips until thoroughly coated. Cover; cook 3 minutes. Top individual servings with cheese.