The grounds for an annulment of marriage are laid out in Family Code sections 2200 (incest), 2201 (bigamy), and 2210 (a - f) (too young, prior marriage, unsound mind, fraud, force, and physical incapacity). I would consult with an attorney to see if a valid argument could be made under any of the above Family Codes.
If proceeding with an annulment is not an option, you will need to proceed with a full divorce proceeding. If you truly believe it will be uncontested though, the process can be extremely easy, and many attorneys may even take the case for a flat fee.
Sign up to receive a 10-part series of useful information and legal advice about the divorce process.