There are several ways you can get Chef Hats for your restaurant:
  1. After successfully completing the Pool Party
  2. After successfully completing the Catering Service
  3. Participating in events may Chef Hats you with various rewards, of which goodies is also a possibility.
  4. Visiting and trying your luck at the Fortune Hut earns you goodies sometimes
  5. Watching ads on the TV can earn you Chef Hats every once in a while (only on Android and iOS devices)
In addition to all that, you can always buy Chef Hats by tapping on the "+" button next to your Chef Hats balance at the right side of the screen.