Place zucchini in a sieve and sprinkle with salt. Toss to combine. Let drain 1 hour and then press on zucchini to release as much moisture as possible. You can also use a cheesecloth and ring out excess moisture. (You don't want the zucchini to be dry, just not soaking wet)
Preheat oven to 325F and grease and line 2 (two) 9-inch round cake pans with parchment paper. You can use 8-inch pans as well but your cake will need to bake a little longer.
In a medium bowl, combine the almond flour, baking powder and salt.
In a large bowl, beat butter with sweetener(s) until well combined. Beat in eggs, lemon zest, zucchini and vanilla extract.
Beat in almond flour mixture until well combined. (If your batter is quite dry, add 1/4 cup to 1/2 cup unsweetened almond milk until it is a thick but spreadable batter).
Gently fold in blueberries. Divide batter between prepared pans and spread evenly to the edges. Bake 35 to 45 minutes, until golden brown around the edges and set on the top. Remove and let cool 10 minutes in the pan, then transfer to a wire rack to cool completely.
In a large bowl, beat cream cheese and butter together until smooth. Beat in sweetener until well combined, then beat in lemon zest.
Beat in 3 tbsp lemon juice. Add remaining tbsp if frosting is too thick.
Place the first cake layer on a serving platter and spread the top with half of the frosting. Add the second cake layer and spread with remaining frosting. Top with fresh blueberries and lemon zest.