Whisk together the diced tomatoes with their juices and the tomato paste in the base of the slow cooker. Stir in the taco seasoning.
Add the chicken breast and thighs to sauce and spoon the sauce over the top. Set the slow cooker on low and cook for 8 hours.
Once cooked, pull apart the chicken with 2 forks and serve in tacos, on tostadas, or in enchiladas. Enjoy!