Without separating rolls, cut rolls in half horizontally; arrange bottom halves of rolls in a greased 9×9-in. baking dish OR place 9 rolls in a 8×8 baking dish. Spread cut side of roll bottoms with horseradish sauce. Place a quarter slice of cheese on the bottom, top with 1/2 slice of turkey which is folded into a little bundle and top with another quarter piece of the cheese. Place the top of the rolls right on top of the assembled sandwiches.

In a small skillet, heat butter over medium-high heat. Add onion; cook and stir until tender, 1-2 minutes. Stir in remaining ingredients except the everything seasoning. Pour the mixture over the rolls. Sprinkle the tops with the everything bagel seasoning. Cover with tin foil and refrigerate for 4 hours or overnight to allow the rolls to soak up that sauce.

Preheat oven to 350°. Take the baking dish out of the fridge and let sit on the counter for 20 minutes.

Bake the covered sandwiches for 25 minutes. Remove the foil and bake until golden brown. (about 5-10 minutes)

Serve on a platter and enjoy!