Place the sliced onions on a sheet tray lined with parchment paper and roast the onions in the oven for a total of 30 minutes.
Every 5 to 7 minutes brush the onions with the balsamic vinegar. Set aside once tender and browned.
In a large sauce pan over medium-high heat with olive oil add in the peppers and garlic and sauté for 4 to 5 minutes.
Next, add in the ground beef and cook until it is completely cooked through. All of the pink should be gone.
Add in the ketchup, mustard, brown sugar, chili powder and Worcestershire sauce and mix until it is completely combined. You may need to add a little water if it is too thick. Keep warm.
Serve the sloppy joe’s on your desired toasted pretzel or brioche bun and top off with different toppings.