Brush a rimmed half sheet pan with half of the melted butter- evenly and all over.
Place two tortillas, side by side, over one of the longest sides so that half is on the pan and the other half hangs over the rim. Add another tortilla to each end, again with half in the pan and half hanging over. Place one tortilla in the center of the pan, so that they cover the bottom of the pan completely.
Sprinkle half of the cheese evenly out overtop of the tortillas. Set aside.
In a medium sized mixing bowl toss the chicken, taco seasoning, beans, and chiles until evenly combined. Spread this mixture evenly out over the cheese. Dot with spoonful's of salsa until it's all used. Sprinkle the remaining cheese evenly out overtop of the chicken mixture.
Add one tortilla to the center of the pan, on top of the filling. Fold up all of the tortillas hanging over from the bottom layer until the filling is completely covered and the sheet pan quesadilla's closed.
Using a pastry brush, brush the top of the tortillas evenly with the remaining butter. Top the prepared quesadilla with another half sheet pan, and gently press down to secure.
Bake, with top sheet pan still in place, at 450° for 20-25 minutes- until the filling is hot and melted and the tortillas are golden brown & crispy.
Carefully remove the hot top pan, and then set the quesadilla aside to rest for a few minutes before slicing and serving.
Serve warm with toppings of your choice.