Preheat oven to 350°F (175°C). Line an 8x4 inch loaf pan with parchment paper, leaving some overhang for easy bread removal.
Whisk almond flour, coconut flour, erythritol, baking powder, and salt in a large bowl until well combined and free of clumps.
In another bowl, beat eggs until smooth. Add melted coconut oil, unsweetened almond milk, lemon juice, lemon zest, and vanilla extract. Whisk until fully mixed.
Pour wet mixture into dry ingredients and stir gently until smooth. Add a splash of almond milk if batter is too thick. Transfer batter to the prepared pan, smooth the top, and bake for 35–40 minutes until a toothpick comes out clean and crust is lightly golden.
Cool bread completely in the pan. For the optional glaze, mix powdered erythritol with lemon juice and drizzle over the cooled loaf. Slice and enjoy!