Pole Vaulting Zombies can vault over any plants in front of them. Therefore, planting Wall-nuts in front of them will be a waste. These zombies also move quicker than other zombies until they vault over a plant.
This level is easier in terms of building an offense because the player now has Potato Mines.
Use the same strategy you always had with Sunflowers and Peashooters to defeat the zombies. Try to plant a column of Wall-nuts closer to the center of the lawn.
When a Pole Vaulting Zombie comes into play, place a cheap plant like a Potato Mine ahead of the Wall-nut to force the zombie to lose its pole and spend time eating the Wall-nut.
If the Potato Mine is still recharging when the zombie appears, using the Sunflower may delay the zombie.
Closer to the end of the level, probably at the final wave of zombies, the defenses should be strong enough to defend all the zombies before they reach the Wall-nuts.
Plants vs. Zombies Wiki has a gallery for Level 1-6.