01 - Preheat oven to 350°F. Line two baking sheets with parchment paper.
02 - In a medium bowl, whisk together the almond flour, rolled oats, baking powder, and salt until evenly distributed.
03 - In a large bowl, beat the softened butter and granulated sugar together using an electric mixer until light and fluffy, about 2 minutes.
04 - Beat in the egg, lemon zest, fresh lemon juice, and vanilla extract until the mixture is smooth and well combined.
05 - Gradually add the dry ingredient mixture to the wet ingredients, mixing on low speed until a soft dough forms and no dry pockets remain.
06 - Gently fold the sliced almonds into the dough using a spatula, distributing them evenly throughout.
07 - Scoop tablespoon-sized portions of dough, roll into balls, and place them 2 inches apart on the prepared baking sheets.
08 - Gently flatten each dough ball with your palm or a fork, then sprinkle the tops with turbinado sugar if desired.
09 - Bake for 12 to 15 minutes, rotating the sheets halfway through, until the edges are golden and the centers are just set.
10 - Allow the cookies to rest on the baking sheets for 5 minutes, then transfer to a wire rack to cool completely before serving or storing.