In a medium saucepan, combine the shredded chicken, salsa, chili powder, cumin, garlic powder, and onion powder. Heat over medium heat until warmed through, about 5-7 minutes, stirring occasionally.
While the chicken mixture is heating, warm the tortillas in a dry skillet over medium heat for about 30 seconds on each side, or until pliable.
Once the chicken mixture is heated, remove it from the heat.
To assemble the tacos, place a generous amount of the chicken mixture in the center of each tortilla.
Top with shredded lettuce, diced tomatoes, cheese, and a dollop of sour cream if desired.
Garnish with fresh cilantro if using, and serve immediately.