Add the ground beef to a large skillet and cook over medium heat, crumbling as it cooks. 

Add half of the diced onion when the meat is nearly cooked through and continue cooking until meat is no longer pink and onions are soft.

Drain grease from the skillet and add the chili seasoning and brown sugar. Stir to coat the meat.

Stir in the tomato sauce. Continue cooking, stirring often, for 5 minutes.

Spoon the meat onto the hamburger buns and top with the shredded cheese and remaining diced onions, as desired.