Which level should I play to get the Nom Nom Nom achievement?

Solution 1:

The first couple levels should be work. There is a couple things you want to focus on

• Focus on sunflowers early on the level, plant them horizontally instead of vertically at first. It is ok for the first one or two zombies to get to the lawnmowers, focus on sunflowers first.
• Plant sunflowers where the zombies got the lawn mowers and start building up chompers
• Don't be afraid to use sunflowers as barriers on the first vertical row if you don't have wall nuts available
• If a chomper is currently eating a zombie and is being attacked himself, remove the current chomper and plant a new one