You can try slicing the grubs out and mounding dirt over the affected area hoping new roots will form...when that doesn't work, lol, dig the plants out and plant new ones.
Later plantings can usually miss the worst of the damage.
The DE dusted on the stems can work for awhile, but only on the bug that lays the eggs grubs form from, the grubs inside the stem won't be killed.
But, it's zucchinis, how many of those things you want anyway?