At the 'Level Selection' screen get an 'Expert' Score on ALL the levels in a Restaurant. When you have unlocked the first level there will be an option on the 'Level Selection' screen that you can click. There are a total of five levels to unlock which is one for each Restaurant.

Business Lunch:
In the Submarine get an 'Expert Score'.

Girls' Night Out:
In the Rail Train get an 'Expert Score'.

Date Night:
In the Cruise Ship get an 'Expert Score'.

Everybody to the Limit:
In the Rocket get an 'Expert Score'.

Summer Camp:
In the Blimp get an 'Expert Score'.