Cook and crumble the ground beef over medium-high heat in a large skillet. When the meat is mostly cooked, drain the grease.
Return the meat to the stovetop and add in the diced onion. Cook for 3 to 5 more minutes to let the meat finish cooking and until the onions soften and become more translucent.
Add the tomato sauce to the skillet. Stir.
Add the BBQ seasoning or sauce and brown sugar. Stir together and continue cooking over medium-high heat until bubbly (about 3 minutes).
Reduce the heat to low and simmer for 5 to 10 minutes. Serve on buns and enjoy!