1. Heat a large skillet over medium-high heat. Coat pan with cooking spray. Add beef to pan; sauté 5 minutes, stirring to crumble. Remove beef; drain. Wipe pan clean with paper towels. Add onion to pan; sauté 4 minutes, stirring occasionally. Add garlic; sauté 1 minute, stirring constantly. Stir in beef, cumin, pepper, and salt.
2. Stir in tomato paste; cook 1 minute, stirring occasionally. Add broth, 1/3 cup water, and tomatoes; bring to a boil. Reduce heat to medium, and simmer 15 minutes or until slightly thick, stirring occasionally. Remove from heat.
3. Place 1 ounce chips in each of 4 bowls, and top each serving with about 2/3 cup beef mixture, 2 tablespoons cheese, and 1 tablespoon sour cream. Sprinkle each serving with 2 tablespoons green onions.