1) Challenge the San Diego Secondary, Especially in the Red Zone
The Chargers' secondary is not that great a unit, whether that is a product of the Chargers struggling to get a pass rush or the unit itself just not having as strong personnel as in past years. Eric Weddle has five interceptions on the year at safety, but collected three of those in one game. Aside from those three, the rest of the secondary including Weddle has six interceptions and on the year are allowing passes to be completed at a 64.3% clip. Over the last three games, they've allowed 247 passing yards to the Chiefs, 232 yards to the Packers, and 298 to the Raiders. They have the 8th-best passing defense in yards, but have allowed 17 touchdowns through the air. In particular, look for the big tight ends to be receiving weapons in the red zone.
2) Get Forte Going Between the 20s
The Bears' running game has been on something that might be called a "hot streak." Over the last six games, the Bears' running game has churned out 152.5 yards per game. This trend probably should continue against the Chargers as the primary method of moving the ball. Given as many touchdowns as the Chargers allow through the air, all year they've allowed 5 rushing touchdowns. Yet they're 24th in the league in rushing yards allowed and are 21st in yards per attempt at 4.5.
3) Pick Up Blitzes
I tried to go a whole post without doing something offensive line-related. Just couldn't do it.
As stated before, most of the sacks by San Diego are generated through blitzing linebackers, not exactly something the Bears have been great at stopping. Barber and Forte will have to do their part in order for any of the passing game to get downfield.