Melt the butter in a large skillet over medium heat. Add the chopped onion and green pepper, sautéing until softened, about 5 minutes.
Sprinkle the flour over the sautéed vegetables and stir to combine. Cook for 1-2 minutes, then slowly add the chicken broth, stirring well. Cook for another 2-3 minutes until the sauce thickens.
Turn off the heat and stir in the shredded chicken, Rotel, and Greek yogurt until well blended.
Spray a 9x13 casserole dish with non-stick spray. Spoon ½ cup of the chicken mixture into the bottom of the dish and spread it out evenly.
Top the mixture with 6 tortillas, followed by half of the remaining chicken mixture and half of the shredded cheese. Repeat the layering process with the remaining tortillas, chicken mixture, and cheese on top.
Bake in the preheated oven for 40-45 minutes until hot and bubbly. The cheese should be melted and slightly golden.
Allow the casserole to rest for 10 minutes before slicing and serving.
Notes
Use rotisserie chicken for convenience.
Letting the casserole sit before serving helps it set and makes slicing easier.
You can use mild or hot Rotel for heat adjustment and opt for fresh tortillas for better texture.