Grounds to get a restraining order against someone else requires evidence of things like abuse, threatening, harassment, and stalking. It follows then that to defend against a restraining order in California you want evidence that counters those things: abuse, threatening, harassment, and stalking.
Relevant phone texts, surveillance footage, emails, witness testimonies, police reports, screenshots, GPS records, and computer and phone records are examples of evidence used to defend against a restraining order. But be careful not to delete or destroy any evidence you think may count against you. That is called perjury and obstruction of justice, which can get you in really deep trouble.