Start by placing the boneless skinless chicken breast at the bottom of your slow cooker.
Sprinkle the taco seasoning evenly over the chicken.
Add the diced yellow onion and sliced jalapeño to the slow cooker.
Pour the entire jar of salsa over the chicken and veggies.
Add salt to taste. Cover the slow cooker and cook on low for 6-8 hours or on high for 3-4 hours.
Once cooked, remove the chicken from the slow cooker and shred it using two forks.
To serve, spoon a portion of the chicken mixture into a large iceberg lettuce leaf and wrap it up.