1. Sauté onion in hot oil in a large skillet over medium-high heat 4 to 5 minutes or until onions are caramel colored.
2. Add ground beef to skillet, and cook over medium-high heat, stirring often, 5 to 6 minutes or until meat crumbles and is no longer pink; drain.
3. Return beef mixture to skillet. Stir in tomato paste and next 2 ingredients, and cook, stirring occasionally, 3 to 4 minutes or until mixture thickens and color darkens. Stir in cola and 1/2 cup water, and cook, stirring constantly, 6 to 8 minutes or until bubbly. Remove from heat, and stir in pepperoncini peppers; add salt and red pepper to taste.
4. Serve beef mixture immediately on buns with coleslaw.