Spray the bowl of a slow cooker with non-stick cooking spray.
Place chicken breasts in an even layer in the bottom of the slow cooker. Sprinkle taco seasoning evenly over the chicken then top with diced tomatoes or salsa. Squeeze lime juice on top of everything. Cover and cook on high for 4 hours or low for 6 to 7 hours.
Remove the lid and shred the chicken with two forks. Serve with tortillas and your favorite taco toppings.
*To make homemade taco seasoning combine 1 1/2 tablespoons chili powder, 1/2 teaspoons cumin, 3/4 teaspoon paprika, 1/2 teaspoon coriander, 1/2 teaspoon oregano, 1/2 teaspoon sea salt, 1/2 teaspoon black pepper, 1/4 teaspoon garlic powder, 1/4 teaspoon onion powder and 1/4 teaspoon crushed red pepper**If using diced tomatoes instead of salsa, you can add 3/4 cup of chopped red onion to the slow cooker for additional flavor.