1. Crumble beef into a large nonstick skillet; cook over medium heat until it starts to sizzle, about 1 minute. Add onion and mushrooms and cook, stirring occasionally, breaking up the meat with a wooden spoon, until the vegetables are soft and the moisture has evaporated, 8 to 10 minutes.
2. Add tomatoes and flour; stir to combine. Stir in water, vinegar, chili sauce and ketchup and bring to a simmer, stirring often. Reduce heat to a low simmer and cook, stirring occasionally, until the sauce is thickened and the onion is very tender, 8 to 10 minutes. Serve warm on buns.

Yield: 8 servings