Start with cooking the bacon in a large heavy bottomed skillet (like a 9 inch cast iron). Reserve some of the bacon grease. Chop bacon into bite sized pieces and set aside.
Cut chicken breasts in half, season generously with salt and pepper. Add chicken to the same skillet you cooked the bacon it. Cook for about 8-10 minutes on each side until fully cooked (165º internally). If using ground breakfast sausage, see notes!
Add the chicken to a stand mixer to shred, or shred by hand. Set aside.Preheat oven to 350 degrees F. Lightly spray a 9x13-inch baking pan with nonstick cooking spray or drizzle bacon grease. In a large mixing bowl stir together 1/2 cup of the cheese, cream cheese, melted butter or bacon grease, milk, seasonings, jalapeños (reserve some for garnish!) and about ⅔ of the bacon (the rest will be garnish), combine well. Stir in the cooked shredded chicken and the thawed hash browns. Spoon evenly into the prepared baking dish.
Bake for 30-35 minutes (see notes on baking times). Remove from the oven, evenly sprinkle with the remaining 1/2 cup of cheese. Bake for an additional 20 -25 minutes, the cheese should be brown and bubbling. Pull from the oven, let it cook just a bit. Garnish with sliced green onions, jalapeños and leftover crispy bacon.
Let the casserole sit for a few minutes to settle, serve and enjoy!