In a medium bowl combine tomato sauce, vinegar, garlic, chili powder, cumin, oregano, and sugar. Mix well and set aside.
In a large skillet over medium-high heat, add olive oil. Cook chicken breasts until golden brown on each side (about 5 minutes per side). Once the chicken is golden brown add the tomato sauce mixture to the pan.
Bring to a boil. Reduce heat to medium-low. Cover and simmer until chicken is fully cooked.
Remove the chicken breasts from the pan (leaving the tomato sauce in the pan). Remove and discard the bone and skin of the chicken breasts. Using two forks shred the chicken. Place the shredded chicken back into the tomato sauce. Cook until the sauce reduces and blends into the chicken. Add cilantro and stir into chicken mixture.
Transfer chicken to a serving bowl and make spoon onto warmed tortillas.