Heat a large skillet over medium heat. Add olive oil, swirling to coat pan. Add onions and brown sugar. Stir to evenly coat onions. Cook for about 45 minutes, stirring frequently until onions are cooked down, tender and a deep golden brown color.
Once cooked down, stir in beef stock and Worcestershire sauce, increase heat to medium high. Cook until the liquid is absorbed. Season with salt and pepper.
Meanwhile, in a large bowl add the ground beef and form into 4 equal sized balls. Preheat pan to medium high heat. Place balls on the pan, smash down and cook for 3-4 minutes per side. Sprinkle salt and pepper on both sides. Place slices of cheese on each burger during the last 2 minutes of cooking.
Make the sauce by combining the ketchup, sour cream, mustard and Thai chili peppers. Mix well
Cook the turkey bacon in the oven at 400 degrees F for 5 mins each side.
Put the sauce on the buns, add the burger patties then the turkey bacon and top with the onions.
If you would like the buns toasted, place them on the pan during the last 2 minutes of cooking as well.