Creating your own Frosted Zucchini Spice Bars is simple when you follow these easy steps:

1. Preheat the Oven: Preheat your oven to 350°F (175°C). Grease and line a 9×13-inch baking pan with parchment paper for easier removal later.
2. Combine Dry Ingredients: In a medium-sized bowl, whisk together the flour, baking soda, baking powder, ground cinnamon, nutmeg, allspice, and salt. Set aside.
3. Mix Sugars and Oil: In a large mixing bowl, combine granulated sugar, brown sugar, and vegetable oil. Mix until well combined.
4. Add Eggs: Beat in the eggs, one at a time, making sure each is fully integrated before adding the next.
5. Incorporate Zucchini and Vanilla: Stir in the grated zucchini and vanilla extract into the sugar-oil mixture until thoroughly combined.
6. Combine Wet and Dry Ingredients: Gradually add the dry ingredient mixture to the wet mixture. Stir until just combined, ensuring no dry lumps remain.
7. Pour Batter: Transfer the batter into the prepared baking pan, spreading it evenly.
8. Bake: Place the pan in the preheated oven and bake for 25-30 minutes, or until a toothpick inserted into the center comes out clean.
9. Cool: Once baked, remove from the oven and let it cool in the pan for 15-20 minutes. Then, transfer to a wire rack to cool completely.
10. Make Frosting: While the bars cool, prepare the frosting. In a mixing bowl, beat together the softened cream cheese and butter until smooth. Gradually add the powdered sugar, mixing until well combined. Add vanilla extract and milk to achieve your desired consistency.
11. Frost the Bars: Once the zucchini bars have cooled completely, spread a generous layer of cream cheese frosting over the top, smoothing it evenly.
12. Slice and Serve: Cut into squares or bars and serve as desired.

These steps will guide you in creating irresistibly delicious Frosted Zucchini Spice Bars that everyone will love.