Cake:
Heat oven to 350 deg. Spread nuts on a baking pan; toast until fragrant, about 10 minutes. Set aside. Lightly oil and line a 9x13-inch baking pan with parchment. In a bowl, sift together flour, cinnamon, baking powder, and salt. Set aside. In the bowl of an electric mixer fitted with paddle attachment, combine oil and sugar. Slowly add half the reserved flour mixture; mix on low until blended. alternate eggs with remaining flour mixture in three additions, beginning and ending with flour. Mix until combined, about 1 minute. Transfer batter to a mixing bowl. Stir in carrots, zest, and reserved nuts. Pour batter into baking pan. Bake until top is golden and firm, about 1 hour.
Icing:
In the bowl of an electric mixer fitted with the paddle attachment, beat the cream cheese and butter until smooth. Gradually add sugar and vanilla; beat on low speed until well blended. Turn mixer to high speed; beat until completely smooth, about 2 minutes more. Use immediately.