Heat oven to 400°F. Coat 15-1/2 x 10-1/2 x 1-inch jelly-roll pan with nonstick vegetable-oil cooking spray. Line bottom of pan with aluminum foil, with 2-inch overhang on short ends. Lightly coat the aluminum foil with the nonstick cooking spray.
Beat together egg whites and salt in large bowl until fluffy. Gradually beat in the sugar until firm, but not dry, peaks form. Sift together the flour and baking powder onto a sheet of waxed paper.
Beat together yolks and lemon extract in medium-size bowl until mixture is thick and lemon-colored, about 3 minutes. Gently fold 1/2 cup of the beaten whites into the yolks to lighten. Fold in the remaining whites and flour mixture until no streaks of white remain. Spread the batter evenly in the prepared pan, making sure its even all around the edges.
Bake in 400°F oven for 8 to 10 minutes or until the top is golden and the cake springs back when lightly touched.
Place sheet of aluminum foil on wire rack. Coat foil with nonstick vegetable-oil cooking spray. Loosen cake around edges with a thin knife; invert cake onto foil. Remove the pan; peel foil from bottom of cake. Let cake cool.
Gently fold together whipped topping and lemon curd in small bowl. Coarsely chop all mandarin orange sections except the five set aside. Fold chopped oranges into lemon curd mixture.
Remove cake with foil to flat surface. Spread filling over entire cake. Using foil as aid, roll up cake from a short side. Place, seam side down, on serving platter. Sift powdered sugar over top of cake. Garnish with reserved mandarin oranges and mint.