Chicken Sloppy Joe

1 (15-oz) can tomato sauce
3 tablespoons brown sugar
1 tablespoon prepared yellow mustard
2 teaspoons apple cider vinegar
1/2 teaspoon salt
1/2 teaspoon pepper
a dash of red pepper flakes (or to taste)
3 cups shredded, cooked chicken
4–6 hamburger buns

In a large saucepan, combine the tomato sauce, brown sugar, mustard, vinegar, salt, pepper and red pepper flakes. Stir to combine and place over medium heat until it starts to bubble. Add in the chicken and cook until heated through. Serve on buns.