Use a large skillet to brown the pork and onion in hot oil over medium heat for 2 to 3 minutes. Drain the fat and stir in the tomato sauce, vinegar, brown sugar, and mustard. Bring to a boil; reduce heat. Cover and simmer for 10 minutes, stirring occasionally. Uncover and cook for another 2 to 3 minutes, until the sauce reaches the consistency you like.
Spoon pork into rolls and top with coleslaw mix and pickles.