Preheat oven to 400 degrees F and line a baking sheet with parchment paper.
Line a mesh colander with a clean dish towel or a few paper towels. Add shredded zucchini then generously salt to encourage draining. Toss and let sit for 15 minutes, then squeeze to remove as much liquid as possible.
As zucchini drains, add flour, baking powder, salt, pepper, garlic powder, and red pepper flakes to a large mixing bowl and sift together. Use a fork or pastry cutter to work in the cold butter until mixture is crumbly.
Add in the milk, egg, cheese, green onion, and drained zucchini. Mix until just combined.
Scoop dough onto the prepared baking sheet spacing about 2 inches apart. The dough should make 12 biscuits.
Bake for 24-26 minutes or until golden on top. Serve warm!