Add the onion powder, tomato sauce, salt, cumin, chili powder, and garlic powder to a 6-quart slow cooker, stirring to combine.

Nestle the chicken into the slow cooker, making sure it is well covered by the tomato mixture.

Cook on high for 3-4 hours or low for 6-7, until the sauce has thickened and the chicken is falling apart.

Remove the chicken and shred with two forks. Add the shredded chicken back to the slow cooker, stirring to combine.