Prepare the Cake:**
- Preheat your oven to 350°F (175°C). Grease and flour a 9x13-inch baking pan, or line it with parchment paper.
- In a medium bowl, whisk together the flour, baking powder, baking soda, cinnamon, nutmeg, and salt.
- In a large bowl, beat the vegetable oil, granulated sugar, and brown sugar until well combined. Add the eggs one at a time, beating well after each addition. Stir in the vanilla extract.
- Gradually add the dry ingredients to the wet ingredients, mixing just until combined.
- Fold in the grated carrots, grated zucchini, and crushed pineapple (if using) until evenly distributed in the batter. If desired, stir in the chopped nuts.
- Pour the batter into the prepared baking pan and spread it evenly.
**Bake the Cake:**
- Bake in the preheated oven for 30-35 minutes, or until a toothpick inserted into the center of the cake comes out clean.
- Remove the cake from the oven and allow it to cool completely in the pan on a wire rack.
**Prepare the Cream Cheese Frosting:**
- In a large bowl, beat the softened cream cheese and butter together until smooth and creamy.
- Gradually add the powdered sugar, one cup at a time, beating on low speed until fully incorporated and smooth.
- Add the vanilla extract and beat until combined. If the frosting is too thick, add a tablespoon of heavy cream to reach your desired consistency.
**Frost the Cake:**
- Once the cake has cooled completely, spread the cream cheese frosting evenly over the top.
- Optionally, garnish with extra chopped nuts, grated carrots, or a light dusting of cinnamon.
**Serve:**
- Slice and serve the cake, enjoying the moist, flavorful cake paired with the rich, tangy frosting.
- Store any leftovers in the refrigerator, covered, for up to 4 days.