Sift together the flour, salt, baking soda, baking powder, and powdered spices.
Beat together the oil, sugar and vanilla for about a minute to aerate.
Add the flaxmeal mixture, beat for a few more seconds to mix, and then add the flour mixture.
Stir with a spatula to get the ingredients well-mixed. The dough will be very stiff. Add the apples and the walnuts and mix well.
Pour the batter into an 8-inch oiled and floured square pan (or use a round cake pan if that's what you have). To make the cake easier to unmold, line the pan with parchment paper or aluminum foil and then oil and flour. I didn't, and trust me, unmolding this cake from the pan was a small battle.
Bake in a preheated 350-degree oven for 40 minutes or until a toothpick inserted in the center comes out clean.
Cool on a rack for at least 10 minutes. Unmold and continue cooling.