Root Beer Sloppy Joes

Name: Root Beer Sloppy Joes
Ingredients: 1 tablespoon olive oil; 3 garlic cloves, minced; 1 lb ground sirloin; 1 1/2 teaspoons chili powder; 3/4 teaspoon salt; 1/4 teaspoon pepper; 1 cup root beer; 2/3 cup tomato sauce; diced green chilis, to taste (1 to 3 Tbsp); 1 1/2 tablespoons Worcestershire sauce; 1/2 cup minced scallion; 4 whole-wheat hamburger buns