Mix together ingredients and set aside.

In a large skillet set over medium-high heat add the bacon and cook until crispy. Remove bacon with a slotted spoon onto a paper towel-lined plate, and set aside.

In the same pan leave about 2 tablespoons of the bacon fat (dispose of the rest) and add in the onions. Cook until soft and golden in color, remove from heat, and set aside.

Preheat oven to 400 degrees and spray a small jelly roll-sized pan lightly with non-stick spray.

Spread an equal amount of mayonnaise on the bottom piece of each roll and place the bottom of the buns into either a 9x13 baking dish or a rimmed baking sheet.

Top the bottoms with turkey, cheese, onions, and bacon, and then top with the tops of the buns.

Pour the butter brown sugar topping mixture over top the buns making sure to try and cover each bun evenly.

Bake for about 20 minutes or until browned and slightly toasty on top.

Set a small skillet over medium heat and add butter.

Once the butter melts add in the dark brown sugar, Dijon mustard, and onion flakes.

Cook until the sugar is dissolved and the mixture is cohesive about 2 minutes.