Clean the zucchini thoroughly and dry them. Then, cut the edges off. Slice the zucchini into ¼" thick slices. Place them on a clean kitchen towel or a set of paper towels, and use another towel to blot them dry as best as you can.
Blanch the zucchini by first adding the zucchini to a pot of boiling water for a minute and then transfer them to an ice bath using a slotted spoon. This deactivates enzymes that typically causes discoloration of zucchini!
Line a baking sheet with a silicon mat or parchment paper. Place the dry zucchini slices on the baking sheet, evenly spaced apart. Place this in the freezer for at least an hour to flash-freeze (this avoids them clumping together later!)
Portion the zucchini and place them into freezer-safe bags or containers.
Freeze Grated Zucchini
Clean the zucchini thoroughly and dry them. Then, cut the edges off. If you plan to use the zucchini for baking, then I recommend slicing it into two halves and scooping out the seeds.
Use a box grater to grate the zucchini on a cutting board. Place the grated zucchini in a clean kitchen towel and wring it dry over your sink to remove excess water.
Then, portion your grated zucchini into the appropriate amounts (I typically do one cup portions). Transfer each portion into an individual freezer-safe bag or container and then place in the freezer.
Notes
You can cook the zucchini directly if you wish. If you wish to use it in casseroles or bake with it, thaw it first by moving the container into the fridge the night before or by placing the container in a bowl of warm water first.
Frozen zucchini will last 6 months (sometimes up to a year!) - I like using mine up at the six month mark since I've observed they get freezer burned thereafter.