Remove the meat from the chicken and shred. Heat the salsa in a skillet over medium heat. Add the chicken and heat until warmed through. Fill the taco shells with the chicken mixture and top with the cheese and cilantro (if using). Serve with the sour cream, avocado, and lime wedges on the side.
Tip: You can use soft corn or flour tortillas instead of crisp taco shells, or leftover roast beef or pork in place of chicken.