Any way to track who has been executing what queries? who has been on my lawn? I have a database in which most of tables are readable for users in one particular security group.

I know most of the users are from my team, but lately I found that it's been used by more and more people, and most of execution occurs from Excel and/or Access.

Out of curiosity, is there any way for me to track who has been tapping into the SQL server and what query they have been running?
Queries aren't logged by SQL Server, unless they meet some criteria that puts them into the default trace or system_health Extended Events session (some details on what they collect here). 

If you can control data access via stored procedures, you can easily add your own logging to those. But that doesn't sound like the case. Otherwise you will have to rely on triggers (for DML, but not SELECT), server-side trace, extended events, auditing, or 3rd party monitoring tools.