Our quick homemade BBQ sauce is lower in sodium than bottled versions. The vinegar in the slaw balances out the sweetness of the BBQ sauce nicely, while the vegetables in the slaw provide an added crunch to the sandwich.
Heat 1½ teaspoons oil in a large skillet over medium-high heat. Sprinkle chicken with 1 teaspoon chili powder. Add chicken to pan; cook 4 minutes on each side or until done. Remove chicken from pan; let stand 5 minutes. Shred chicken into large pieces with 2 forks.
While chicken cooks, heat 1½ teaspoons oil in a medium saucepan over medium heat. Add ½ cup onion; sauté 5 minutes. Add remaining 2 teaspoons chili powder, tomato sauce, 1 tablespoon vinegar, 1 tablespoon sugar, ½ teaspoon salt, and ¼ teaspoon pepper to pan; bring to a boil. Reduce heat, and simmer 5 minutes. Stir in chicken; keep warm.
Combine remaining 1 tablespoon oil, remaining ¼ cup onion, remaining 2 tablespoons vinegar, remaining 1½ teaspoons sugar, remaining ¼ teaspoon salt, remaining ¼ teaspoon pepper, and coleslaw. Top bottom halves of buns evenly with chicken mixture, slaw, and top halves of buns, or serve slaw on the side.