Zen mode is a time based mode in which you have to hit the required score.
There are no bombs, and you will not lose any lives.
The trick to Zen mode is combos. Without combos, 200 fruits do not appear in the required time. Therefore without combo's it is not possible to do.
My favourite tactic was to keep my hands in the middle of the screen. When the fruits pop, a lot of the time you'll get a cluster of fruits lined up. Wait for your moment, then slice from right/left or left/right. Depending on the amount of fruits launched, you can hit some pretty big combos here.
Unfortunately, some of it is luck based, as it depends on how the fruit is launched for you. If your unlucky, you'll only get 3 in a cluster. If you're lucky, you can get 6.