To do that, instead of using a notification, you can setup an Action Group calling a logic app.
You can customize as you like the body of the email in the logic app.
Logic apps have a built in trigger for Azure Monitor and a variety of email senders.
You can follow this article for more help.
----------
Please remember to "Accept Answer" if any answer/reply helped, so that others in the community facing similar issues can easily find the solution.