California Vehicle Code Section 21801(a)
"The driver of a vehicle intending to turn left or complete a u-turn upon a highway or turn left into public or private property or alley shall yield the right of way to all vehicles approaching from the opposite direction which are close enough to constitute a hazard at any time during the turning movement and shall continue to yield the right of way to the approaching vehicles until the left or u-tun can be made with reasonable safety"
The Failure to Yield Defenses
First, a Traffic Collision Report conclusion is hearsay and cannot be admitted in court. Just because the TCR says the other party is at fault does not mean they have to accept liability. Second, In almost every case the insurance company who represent the driver at fault will allege excess speed, inattention, overreaction or that they had "control of the intersection". They will rely on CVC Section 21801(b).
California Vehicle Code Section 21801(b)
This section states that the driver, after "having given a signal" my turn left and the other vehicle (the motorcyclist) shall yield the right of way to the turning vehicle. What? Yes, they will argue that they put on their turn signal, initiated the turn and you punched it to beet the turning vehicle thereby causing or contributing to causing the collision. They will then say that you are say 25% at fault.
If they do not accept and stipulate to 100% liability in writing. You may be required to get a motorcycle accident attorney, file a lawsuit and take depositions. But it all depends on the extent of your injuries and damages to determine if it tis worth it.