Preheat oven to 350 degrees F. Lightly grease a 9-10 inch round cake pan. Place pineapple slices on the bottom of the pan.
In a large bowl, beat the eggs, sugar and vanilla on high speed for about 8 min. Slowly add flour. Using a spatula fold in gently. Continue until all of the flour mixture is incorporated.
Add chopped walnuts.
Carefully spoon mixture into a pan cake.
Bake for 25-30 minutes or until toothpick inserted in center comes out clean.
Cool for at list 10 minutes, then turn the pan over onto a serving plate. Wait 30 seconds then lift the pan off.