Place the chicken breasts in the slow cooker.
In a small bowl, stir together taco seasoning and olive oil to make a paste. Rub this evenly over the chicken.
Pour the salsa and water evenly over the top of the chicken.
Cover with the lid and cook on low for 4-5 hours or on high for 2–3 hours, until the chicken reaches 165°F and is very tender.
Transfer the chicken to a large bowl and shred with two forks. Return the shredded chicken to the slow cooker and stir to coat.
Warm the tortillas in a dry skillet over medium heat for about 30 seconds on each side, or until pliable.
To assemble each taco, place shredded chicken onto a warm tortilla, then top with pico de gallo, shredded lettuce, finely grated white cheese, extra cilantro leaves, and a squeeze of fresh lime juice.