In a bowl, combine the salsa, canned diced tomatoes with chilies, and taco seasoning, stirring until well mixed and the seasoning is fully incorporated with no lumps. This ensures even flavor distribution throughout the cooking process rather than having dry seasoning spots in the finished dish.

Spread the diced onion evenly across the bottom of your crockpot, then arrange the chicken breasts on top in a single layer. Pour the sauce mixture from Step 1 over the chicken, making sure all pieces are submerged or well-coated. The onions on the bottom help prevent sticking and create a flavorful base.

Cover and cook on low for 7-8 hours, or on high for 3-4 hours, until the chicken is completely tender and shreds easily with a fork. I prefer cooking on low overnight as it allows the flavors to develop more deeply and the chicken stays incredibly moist.

Using two forks or a shredding tool, shred the chicken directly in the crockpot, breaking it into bite-sized pieces. Stir everything together thoroughly so the shredded chicken absorbs all the flavorful juices and sauce. Let rest for 2-3 minutes before serving so the flavors fully meld.

Spoon the shredded chicken and sauce mixture from Step 4 onto warm tortillas and top with your favorite taco toppings such as shredded cheese, sour cream, lettuce, or cilantro. The chicken mixture can also be served over rice, in nachos, or as a filling for burritos.