You need to focus more on talking about the role of a commercial lawyer rather than your commercial awareness or how law firms operate as a business.
Elaborate on how commercial lawyers advise their clients, work with other lawyers on deals, represent their clients in negotiations, are involved in business development and training etc. You could pick a deal the firm has done recently and use it as an example to break down how commercial lawyers would have been involved in it at different stages and in what capacity.
This breaks down a commercial lawyer's role fairly well- you can use it as a springboard for your answer.