Add the chicken breasts into the slow cooker and season with the garlic powder, ancho chili powder, chili powder, onion powder, salt, cumin, and oregano.
Add the diced onion and can of diced tomatoes on top.
Cover and cook on low for 6 hours or on high for 4 hours until the chicken is fall-apart tender.
Shred the chicken with two forks in the slow cooker and stir together with all the juices.
Serve in warmed corn or flour tortillas tacos, burritos, or nachos.
Notes
You can use chicken thighs instead of chicken breasts if you prefer.
If you don’t have ancho chili powder, double the amount of regular chili powder.