Preheat oven to 350 degrees. Spray a 9-inch diameter springform pan with nonstick olive oil spray. Place parchment paper round in bottom of pan and spray paper.
Grind pecans in processor using pulse button until finely ground - but not powdery. Combine pecans, flour and baking powder in medium bowl and set aside.
Using electric mixer, beat eggs in large bowl until frothy, about 2 minutes. Gradually add sugar, beating until light, thick and a pale yellow color (4 minutes).
Gradually add walnut flour mixture, and then add orange juice, orange zest and olive oil. Beat until blended. Transfer batter to prepared pan.
Place pan on rimmed baking sheets and bake until tester inserted into center comes out clean, about 1 hour. Cool cake completely in pan on rack.
Release pan side, carefully invert cake onto platter and remove parchment paper. Sprinkle powdered sugar on top of cake and serve with fresh orange whipped cream (below) on top or on the side.
Combine whipping cream, powdered sugar, orange zest and juice in medium bowl. With electric mixer beat to soft peaks.
Whipped cream can be made 3 hours ahead. Cover and chill. Rewisk before using.