In a skillet over medium heat, add olive oil. Once hot, add the shredded chicken, chili powder, cumin, garlic powder, onion powder, salt, and pepper. Stir to combine and cook for about 5 minutes, until heated through.
While the chicken is warming, prepare the fresh salsa by combining diced tomatoes, red onion, and cilantro in a bowl. Season with salt and pepper to taste.
Warm the tortillas in a dry skillet or microwave until soft and pliable, about 30 seconds.
Assemble the tacos by placing a generous portion of the seasoned chicken on each tortilla. Top with shredded lettuce, fresh salsa, and avocado slices.
Serve with lime wedges on the side for squeezing over the tacos.