Method
Shred cheese (about 3 cups); reserve. Cut a diagonal pocket in the top of each chicken breast half; stuff each with 1/4 cup reserved cheese. Refrigerate.
To make salsa, mix onion and next 5 ingredients; stir in 1/2 tsp salt. Gently fold in avocado; reserve.
Per Order: Brush 1 chicken breast with butter; lightly season with salt and pepper. Bake at 500 degrees F until chicken is browned and just firm to the touch; about 10 minutes. Garnish with 1/4 cup reserved salsa.