Coat chicken breasts with 1 tablespoon olive oil. Sprinkle with taco seasoning and bake at 350 degreed for 30 minutes, or until done.
When chicken is cool enough, shred chicken with fork. In a sauce pan, cook onions in remaining olive oil until tender. Add chicken and tomato sauce and remaining seasonings and simmer on medium low, covered for 15 minutes.
Warm tortillas. To build tacos, scoop a spoonful of chicken into each tortilla. Add lettuce, cheese, olives and then avocado.