Toast the coriander seeds in a saucepan on medium-high heat until they become fragrant. Grind them in a mortar and pestle.
Mix the dry ingredients. Beat the egg yolks with the sweetener and the olive oil until creamy. Beat the egg whites until they form stiff peaks. Chop the strawberries.
Incorporate sifted flour and egg white into the egg yolk mixture by gradually alternating between flour and egg white. Gently fold them in with a spatula. Finish with egg white.
Dust the chopped strawberries with a little bit of tapioca flour, then add them to the batter and gently fold them so they are evenly distributed.
Pour the batter into the baking dish and bake at 350F/180C for 35 minutes. The cake will not be soft to the touch; it will get golden brown on top.
Beat the mascarpone cheese with sweetener if using (I don't), vanilla, and the lemon zest or lemon extract, until it's thick (use an electric mixer). Refrigerate until the cake is ready and completely cold.
When the cake is ready, let it rest on a cooling rack until completely cold. I like to slice and remove the edges to see the beautiful texture of the cakes on all sides.
Spread the frosting on top, then portion it into small squares. From the dimensions I had, I got 36 small tapas-style cakes. Decorate each cake with chopped strawberries and ground toasted walnuts if using.