In 3 1/2 to 4-quart slow cooker, combine all ingredients except tomato paste and buns.
Cover; cook on low setting for 8 to 10 hours.
With slotted spoon, remove meat from slow cooker. Shred meat with 2 forks; return to slow cooker. Stir in tomato paste.
Cover; cook on high setting for 5 to 10 minutes or until hot. To serve, spoon about 1/2 cup mixture into each bun.