Pistachio Pudding Cake (Green Slime)

When I worked, my coworkers used to ask for this cake, which one of the guys named Green Slime Cake, each St. Patrick's Day.
1 pkg. white or yellow cake mix
1 pkg. pistachio instant pudding mix
3 eggs
1 c. club soda
1 c. oil
1/2 c. chopped nuts

Blend all ingredients in large bowl; beat 2 minutes at medium speed. Bake in greased & floured 10" Bundt pan at 350 degrees for 50 minutes. Cool 15 minutes on wire rack; remove from pan & cool completely on rack. Cut cake into 3 layers. Spread about 1 c. frosting between layers; spoon rest into center. Chill. Garnish with chopped nuts.

Frosting:
1-1/2 c. cold milk
1 envelope Dream Whip
1 pkg. pistachio instant pudding mix

Whip until thickened, about 5 minutes.