There are a few steps you can take to prevent the zucchini lasagna from becoming watery. First, slice the zucchini into very thin strips (3mm or 1/8 inch). Then, generously salt the slices with salt. This is an important step since salt draws water out of the zucchini. It takes about 15 to 20 minutes for the zucchini to "sweat" water. At that point, you'll thoroughly dab the zucchini with paper towels to remove water.