Preheat the oven to 350º. Place 1 cup shelled roasted, unsalted pistachio meats into a blender or food processor and pulse to grind into a flour. Be careful not to pulse too long, as they can quickly become pistachio butter. Sift into a bowl, return larger pieces to the blender, and repeat process until you have one cup pistachio flour. You will have extra, which you can use within the trifle.
In a large bowl, whisk the flour, pistachio flour, lemon zest, baking soda, and sea salt until completely combined and clump free. In a medium bowl, whisk together olive oil, honey, milk, rosewater, eggs, and vanilla bean paste until completely integrated.
Pour wet mix into dry and fold together with a silicone spatula, stirring until combined. Pour into an oiled (or buttered), floured 8" cake pan and bake 20-22 minutes, until cake is domed and golden, and a knife or cake tester inserted in the center comes out clean. Remove from oven and increase oven temperature to 425º for the roasted apricots (below)
Cool on a wire rack until no warmth remains, then run a butter knife around the edges of the pan to loosen the cake and turn over to remove from pan. Rest on a cutting board, and slice cake in half horizontally, creating two 8" cake circles. Grid each to create 1" squares of cake, and cut accordingly. Set aside.