Preheat oven to 180 Cº (350 Fº).
Grate zucchini and squeeze water using a clean towel (also paper towels work).
In a bowl stir together 1 egg, Greek yogurt, shredded zucchini (squeezed from the water) and sweetener of choice.
Add to wet keto mixture almond flour, protein powder, cocoa powder, baking powder and pinch salt.
Pour in milk of choice and mix ket brownie batter. If necessary add more milk (see notes*).
Cover with parchment paper a 16 x 10 cm (6.2 x 4 in) baking pan and transfer zucchini brownie batter in baking pan.
Bake in hot oven for 20 to 30 minutes (it may take as long as 35 minutes). To check if keto zucchini brownies are baked through stick toothpick in the center of brownies: if it comes out wet the brownies needs more time.
Let small batch brownies cool before slicing.