I start by mixing the salsa, diced tomatoes with chilies, and taco seasoning in a bowl. This ensures the seasoning spreads evenly across the chicken. The mixture should look well combined and slightly thick.
Next, I place the diced onion and chicken breasts into the slow cooker. I pour the prepared sauce right over the top so the chicken is fully coated. This helps lock in moisture as it cooks.
I cook everything on low for about 7–8 hours or on high for 3–4 hours. Once the chicken is tender, I shred it directly in the crockpot and mix it into the juices. This step makes the chicken extra juicy and flavorful.