LAMP performance tuning with a focus on PHP and MySQL

We've recently had some performance issues on a hosted site without having a huge volume of users accessing it so we believe there are some issues in our PHP/MySQL that need to be identified at a minimum and ideally fixed.

We also want the person selected to apply best practice security and performance tuning measures. Ideally we'd like to see this turned around in 1 max 2 days from starting as the site isn't huge and we're concurrently developing and deploying functional releases that we don't want to put on hold for too long.

Ideally we'd like to see a specialist in this area with relevant experience and a good track record of doing the same things for others.