Shred the chicken, slice the onion into thin strips (reserve a quarter of the onion for blending), and wash and chop the lettuce.

Heat a pan with oil, add the onion and cook until translucent without burning, then add the shredded chicken and cook until slightly browned.

Once the chicken is ready, add the blended sauce, cover, and simmer on low heat for 3 minutes. Turn off the heat and it's ready! Serve with tostadas, lettuce, and sour cream.