Lewis has coached for 22 years in the NFL. He announced his retirement after the 2004 season, while working as the offensive coordinator for the Detroit Lions.
Lewis, who has extensive experience in the West Coast offense run by coach Jim Zorn, was hired by the Redskins on Wednesday.
The Redskins have yet to score 30 points in a game since Zorn became coach last year. They rank 27th in the NFL in scoring this season, averaging 14 points.
Executive vice president for football operations Vinny Cerrato said Zorn welcomed the idea of some offensive help. Cerrato told the Redskins' Web site that Lewis is "not a threat at all" to Zorn's job security.