Place all ingredients except buns in a gallon size zip-top bag. Label and freeze.
When ready to cook, thaw in refrigerator overnight.
Place contents of bag in a slow cooker. Cover and cook on low 8-10 hours.
Shred meat and discard any fat.
Serve on toasted buns or rolls. Add sliced provolone cheese, sliced avocado, and mayonnaise, if desired.