I'm a chef, my boss just fired my coworker for no reason, what's the best course of action?

My boss just fired my coworker for no reason, what's the best course of action? We are all part time seasonal cooks at a restaurant. I was told by my boss that he was fired but no real reason was given. I know he didn't want to do something as simple as talk to him about it, but just immediately fired him. The cook in question was a bit of a loner, didn't really talk to people in the kitchen but he was good at his job, showed up on time and always worked hard. He was one of our newer staff and I've seen him work his butt off to improve his technique and help out his colleagues. I know we are all part time cooks and the boss was a bit of an asshole. He's a millionaire and I don't think he's had a real job since he was in high school.<br><br>What are some good actions I could take to help my coworker get rehired or to get revenge against my boss? Should I report him to the HR department? Do I tell my colleagues to do a walkout? I'm not really sure where to go from here.