Place the 3 boneless skinless chicken breasts about 2 lbs total in a saucepan and cover with 4 cups chicken broth for poaching. Add 1 tsp salt and bring to a gentle boil over medium-high heat. Reduce to a simmer, cover, and cook for 15–18 minutes, until the 3 boneless skinless chicken breasts about 2 lbs total is cooked through and no longer pink in the center (internal temp 165°F). Remove the 3 boneless skinless chicken breasts about 2 lbs total and let it rest for 5 minutes, then shred it with two forks. Reserve the poaching broth.

Preheat your oven to 350°F. In a large skillet over medium heat, melt the 4 tbsp unsalted butter. Add the diced yellow onion and 1 green bell pepper and cook, stirring occasionally, for 5–6 minutes until softened. Add the minced garlic and cook for 1 minute more until fragrant.

Add the 1 can diced tomatoes with green chiles (Rotel) do not drain (with their juices), 1 can cream of chicken soup, 1 can cream of mushroom soup, and 1 cup sour cream to the skillet. Stir everything together until fully combined and smooth. Add the 2 tsp chili powder, 1 tsp cumin, ½ tsp smoked paprika, and ½ tsp black pepper. Stir well and taste — adjust seasoning as needed. If the sauce seems very thick, stir in a splash 2–3 tbsp of the reserved chicken broth to loosen it. Remove from heat.

Grease a 9x13-inch baking dish with cooking spray or a thin layer of unsalted butter. Spread a thin layer of sauce (about ½ cup) across the bottom of the dish to prevent sticking.

Arrange half of the torn corn tortilla pieces in an even layer over the sauce, overlapping slightly to cover the bottom. Spread half of the shredded 3 boneless skinless chicken breasts about 2 lbs total over the tortillas, then ladle half of the cream sauce over the 3 boneless skinless chicken breasts about 2 lbs total. Sprinkle with half of the shredded cheddar cheese and half of the shredded Monterey Jack cheese.

Repeat the layers: remaining tortillas, remaining boneless skinless chicken breasts about 2 lbs total, remaining sauce, and finally the remaining shredded cheddar cheese and 1 cup shredded Monterey Jack cheese on top. The cheese layer on top should be generous and even.

Cover the dish tightly with aluminum foil and bake at 350°F for 30 minutes. Then remove the foil and bake for an additional 15 minutes, until the cheese on top is bubbly, golden, and beginning to brown at the edges.

Remove from the oven and let the casserole rest for 10 minutes before cutting and serving. This helps the layers set so it slices cleanly. Garnish with sliced green onions and fresh fresh cilantro roughly chopped if desired.