Prepare the Hotdog Chili by sautéing the minced sweet onion until translucent, then add ground beef and cook until browned. Stir in chili seasoning, ketchup, and water; simmer for 15-20 minutes.

Make the Creamy Slaw by combining coleslaw mix, mayonnaise, apple cider vinegar, and sugar in a large bowl. Season with celery seed, garlic powder, and pepper. Mix and chill for at least 10 minutes.

Form and cook the patties by dividing ground chuck into four equal portions and pressing into thin patties. Season and cook in a skillet or grill for 4-5 minutes each side until browned.

Melt cheese if desired by adding a slice to each patty in the last minute of cooking. Cover until melted.

Assemble the burgers starting with mustard on the bun, then the patty, hotdog chili, creamy slaw, and diced onions.