For the sauce:
7-8 fresh Hatch green chiles
1/2 onion
1 garlic clove
1 cup stock
1 teaspoon Mexican oregano
pinch of cumin
1/4 teaspoon salt (plus more to taste)
freshly cracked black pepper
olive oil

For the enchiladas:
1 large chicken breast
8 corn tortillas
2-3 tablespoons finely chopped onion
1 cup shredded Jack cheese

7 -8 fresh Hatch green chiles 1/2 onion 1 garlic clove 1 cup stock 1 teaspoon Mexican oregano 1/4 teaspoon salt (plus more to taste) 1 large chicken breast 8 corn tortillas 2 -3 tablespoons finely chopped onion 1 cup shredded Jack cheese

Start by giving the Hatch chiles a good rinse. Roast the chiles in a 400F oven for 20-30 minutes.
To poach the chicken, cover the chicken breast with cold water and bring to a boil. Once boiling, reduce heat and let simmer for 20 minutes or until the chicken is cooked through. Once cooked, set aside to cool and then shred using two forks. You can optionally add a half onion, cilantro sprigs and a pinch of salt to the poaching liquid for additional flavor.
Once roasted and cooled off a bit, de-stem and de-seed the chiles. You can also pull off and discard any loose bits of skin from the chiles. Add the roasted chile pieces to a blender along with a splash of water or stock and combine well.
Finely dice the 1/2 onion, reserving a few tablespoons of the chopped onion for the insides of the enchiladas. Saute the majority of the chopped onion in some oil over medium heat. Once it has softened add a minced garlic clove and cook for an additional minute or so. Add the chiles from the blender along with: 1 cup stock, 1 teaspoon Mexican oregano, a pinch of cumin, 1/4 teaspoon of salt, and some freshly cracked black pepper.
Bring the sauce to a simmer and take a taste for seasoning. I added another generous pinch of salt to this batch but it will depend on which stock you're using. You can always adjust the consistency of the sauce by adding more stock to thin it out, or by letting it simmer for a bit to thicken it up.
Heat the corn tortillas in the oven for a few minutes. (Or nuke them in some damp paper towels for 60 seconds.) Prepare the baking dish by adding a bottom layer of the Hatch sauce to prevent sticking.
On a plate, add a couple spoonfuls of the Hatch sauce. Dredge a tortilla in the sauce, flip, and then fill with shredded chicken, onion, and plenty of shredded cheese. Roll tight and place seam side down on the baking dish. Keep going until the chicken is gone. Add the remaining sauce on top of the enchiladas along with a final layer of cheese. I usually give the enchiladas a jiggle so that you get plenty of sauce between them.
Bake for 10 minutes in a 400F oven or until the cheese is completely melted. Serve immediately. Optional garnishes include freshly chopped cilantro, a squeeze of lime, and a drizzle of Crema.