Not a hard achievement at all. When at the main menu just add an extra controller on a guest account and choose versus (couch).
Now choose a map (I did Sushi city 10 times), and let your team serve a couple of meals, so it gains more coins then the guest team. At the end of the match you'll gain 10% towards this achievement. Repeat another 9 times to gain this achievement. When you're done with that. You can win (or lose) another five matches in versus to gain:
When you don't have a second controller, find someone online through this site! When you both need the achievement you'll rack up 20 matches and automaticly gain "It's a Cookoff".