I cannot recall the source. This recipe is tried and true.
3 pounds boneless, skinless chicken breast
2 tablespoons chili powder
1/2 teaspoon oregano
4 tablespoons fresh squeezed lime juice
Soak chicken in salt water for 1 hour. Pat dry. Brush the chicken with vegetable oil.
Make a paste from the chili powder, oregano and lime juice. Rub the paste over the chicken and refrigerate for several hours. Grill. Slice very thin after grilling. Make your fajitas.