This tip is from ‘The Kitchn‘.
Though you can technically freeze zucchini as is, we recommend taking the time to blanch it first. Blanching inactivates the enzymes that cause the vegetable to become mushy and discolor over time, even in the freezer.
Put a large pot of water over high heat and set another bowl with ice water near the stove. Have a slotted spoon handy to scoop the zucchini out of the pot.
While you’re waiting for the water to boil, chop your zucchini into rounds, wedges, or any other shape you normally cook with. Remember that you’re going to be dumping the frozen zucchini directly into the soup or Chilli you’ll making, so aim for uniform bite-sized pieces.
When the water comes to a boil, add your cut vegetables to the pot and begin timing. You’re going for crunchy al dente. For small wedges like those shown here, test them after a minute. For larger rounds, it will take more like 1-2 minutes.
Note: Unlike blanching vegetables that you’ll eat right away, this blanching water should be unsalted. In this case, salt absorbed into the vegetables would cause the cell walls to keep breaking down over time, which would result in the kind of mushy veggies we’re trying to avoid.
Scoop the vegetables out of the water and transfer them immediately to the water bath to stop the cooking and then drain. For large amounts of zucchini, do this in several batches. If we have the time and energy, we like to spread the zucchini out in a single layer on a parchment-lined sheet tray to freeze them before getting packed into bags. This prevents the pieces from freezing to each other and makes for more even cooking on the other end.
Otherwise, you can transfer the drained zucchini right into bags and tuck them into your freezer. Keep them toward the back of your freezer where the temperature is more constant.