Crumble sausage into a deep, 3-quart casserole and add onion.
Heat, uncovered, on medium for 9 minutes or until sausage is cooked and onion is tender.
Drain off excess fat.
Add cabbage, tomatoes, sugar, oregano, salt and pepper.
Stir to combine.
Cook, covered, on medium for 10 to 12 minutes or until cabbage is tender.
In a small cup mix flour and water until smooth.
Gradually stir flour mixture into sausage mixture.
Cook, uncovered, on medium for 4 minutes, stirring frequently until thickened.