Combine flour, baking powder, baking soda and salt.
In a large bowl, mix oil, eggs, vanilla, sugar, cinnamon, and nutmeg. blend in pineapple, zucchini and carrots. Stir flour mixture into zucchini mixture. Fold in chopped walnuts. Pour batter into two greased and floured 9 x 5 loaf pans.
Bake at 350°F for 1 hour. Cool on wire racks.
Tip: If you have an abundance of zucchini on hand, grate the zucchini and some carrots and store them in freezer bags (2 cups zucchini and 1/2 cup of carrots). This freezes really well and you will always have the zucchini and carrots on hand to make this bread in the fall and winter months. This will also save time during the preparation.