In a large heavy skillet lightly coated with non-caloric vegetable cooking spray, sauté ground meat of choice and onions over moderate heat just until ground meat is lightly browned, stirring frequently. Pour off any excess fat.
Reduce temperature slightly; add chili sauce, vinegar, water, chili powder, mustard, Worcestershire sauce, brown sugar, liquid smoke, if desired, and salt and pepper to taste, mixing well. Bring mixture to a simmer; continue simmering, uncovered, for 35 to 45 minutes to blend flavors.
To serve, arrange two halves of a bun on each plate. Spoon barbecue mixture over each bun half, dividing evenly. Garnish as desired and serve as an open-face sandwich. Or, spoon barbecue mixture onto the bottom half of each bun; cover each with the top half of the bun. Garnish as desired.
Variations: Top each barbecue-filled bun half with a slice of sharp Cheddar or Monterey Jack or other desired cheese; transfer sandwiches to a baking sheet and bake in a preheated moderate oven (350 degrees F.) for about 7 to 8 minutes or broil for 2 to 3 minutes about 6 inches from heat source until cheese has melted.
Add a few drops hot pepper sauce to meat mixture.