Roast Beef Wraps

1 small red onion , thinly sliced 1 tablespoon distilled white vinegar 1/3 cup low-fat sour cream 1/3 cup light mayonnaise 2 tablespoons bottled white[...]

2 flour tortillas (10-inch diameter) or 2 one 4 1/2-ounce sheet soft lavash bread, trimmed to 20-inch length 8 ounces thinly sliced roast beef 1 (7 ounce) jar[...]