In 3-quart saucepan, heat oil over medium-high heat. Add onion and cook, stirring occasionally, until softened and lightly browned, about 8 minutes. Stir in chili powder, dry mustard, and cinnamon. Cook 1 minute. Add ketchup, honey, orange juice, and vinegar. Bring mixture to a boil and add sliced pork tenderloin. Reduce heat to low and simmer, stirring occasionally, for 15 minutes.
Place half of BBQ-pork mixture in a resealable container; cool to room temperature, cover, and place in freezer. Place 4 sandwich buns in resealable storage bag, and store in freezer.
Divide remaining BBQ pork among remaining sandwich buns, and serve with coleslaw and pickles, if desired.
Defrost BBQ pork in refrigerator overnight. Reheat mixture in saucepan over medium-low heat, or microwave until heated through. Defrost sandwich buns to room temperature.