Add chicken breast to slow cooker and top with approximately 3 cups of salsa verde, to cover chicken. Cook on low for eight hours overnight.

Shred chicken and drain excess liquid by straining. Add an additional 2 to 3 cups salsa verde to shredded chicken and mix.

Preheat over to 400.

Spray large skillet and heat on high. Brown corn tortillas on both sides. Respray pan between batches (my skillet fit 2 at a time). Cook all 18 tortillas.

Using a 13x9 glass baking dish, line bottom with approximately 1 cup salsa verde.

Add one layer of 6 corn tortillas.

Add 1/3 chicken mixture spread in a layer.

Add 1 layer of muster cheese slices, approximately 8 slices.

Repeat layer of tortillas, chicken, and muster cheese 2 more times for a total of 3 layers. Your final layer should be of sliced muster cheese.

Completely cover cheese layer with salsa verde, enough to cover.

Bake at 400, uncovered, for 30 minutes, until bubbly.

Sprinkle shredded Oaxaca cheese on top and bake for another 10-15 minutes.