Combine ranch dressing, sour cream, 1 teaspoon taco seasoning and salsa in a small bowl. Cover and refrigerate until serving.
Toss chicken with remaining taco seasoning. Cover bowl loosely with baking paper or cling wrap. Microwave chicken until chicken is heated through, about 2 to 3 minutes.
Warm the tortillas in a frying pan for about a minute on each side. Place a scoop of chicken on the tortilla then top with lettuce, tomato, spring onion, olives, avocado, cheese and a spoonful of the ranch dressing mixture.
You can use a left over roast chicken, you can buy a hot roasted chicken or you can boil chicken breast for an hour then shred it with two forks. I prefer using leftover.