Poach chicken. Place chicken in a saucepan, and cover with water. Bring to a boil, then reduce the heat to simmer for 10-12 minutes or until the internal temperature of the chicken reaches 165°F/74°C. I use the kitchen thermometer to check as overcooked chicken will be dry.
Transfer the chicken to a cutting board or bowl, and shred it with 2 forks.
In a skillet, heat oil and sauté the onion until it’s soft and translucent (3 minutes).
Add the garlic, and sauté for 30 seconds. Add cumin, chilli powder, and salt. Cook for 1 more minute.
Add salsa, and just mix it in (if necessary, you can add a splash of water) and let it warm up.
Add the chicken, and mix it in with the sauce. Simmer for 2-3 minutes.
Serve in warmed up tortillas or taco shells with your favorite toppings.
Frozen Chicken. You can use this method to boil frozen chicken breasts, it will take longer for the water to boil, and additional simmering time to cook them completely.