El Gringo Mexican
The Chimichanga is a specialty, and worth trying if you are into fried Mexican. The con queso isn't, and just tastes like melted cheese.
If you feel like ice-cream, you have a choice of Simmos at the beach, or Gelato in town. The Gelato is homemade and relatively cheap, and they make their own chocolate spoons and bowls.
Busselton has an amazing amount of large licenced cafes, serving modern Australian style cuisine. You have plenty of choice if you take a walk down the main street.