Hi Chef,
You can tap on the empty plots next to the Restaurant to see the Coins and Expansion Tools required to buy the plots. Click on 'Expand' to buy new areas or plots if you have met all the requirements.
However, if you don't have the required Coins and Expansion Tools, you can always purchase the plot by using Cash.
Additionally, you can earn or buy Expansion Assists to help you with expansion if you are short of Tools.