Structure is key to succeed in interview.
In general, the philosophie is "a unique client issue requires a unique approach", so let's avoid using strandard framework learned from the book. They are a good way to start learning for very beginners but are too theoretical to properly fit with a real case.
Quick tips to build a MECE structure :
1. Make sure you capture the key topics : I highly recommand here to put yourself in your clients shoes and think about the topic you need to cover before making a reasonable decision. This will facilitate the identification of key topics, and somehow will help to prioritize them
2. Make sure you don't cover unrelevant topics : this is particularly happening when you try to apply standard framework, and force some "blocs" in the structure. In reality, depending on the situtation and the issue, the answer to provide can vary a lot and that's why you need to really think by yourself and challenge the topics you want to cover with the following question " if I spend time on this topic, will this bring absolutely key information for the final recommandation". if the answer is not clearly yes, then you should drop the topic.
Hope this help, don't hesitate to reach me, I have developped a full set of exercice dedicated to working the structure.