Preheat oven to 400°F (200°C). Grease a 12-cup muffin tin or line with paper liners.
In a large bowl, whisk together the flour, baking powder, baking soda, salt, allspice, cardamom, cinnamon, ginger, and nutmeg.
In a separate bowl, whisk together the brown sugar, olive oil, and eggs until well combined.
Fold the wet ingredients into the dry ingredients just until combined. Fold in the grated carrots, pineapple, walnuts (if using), and raisins (if using).
Scoop the batter into the prepared muffin cups, filling them about ¾ full.
For the crumble topping (optional): In a small bowl, mix together the butter, oats, brown sugar, flour, and salt until crumbly. Sprinkle the crumble topping over the muffin batter.
Bake for 18-20 minutes, or until a toothpick inserted into the center comes out clean.
Allow the muffins to cool in the tin for 5 minutes, then transfer to a wire rack to cool completely.
For the cream cheese frosting: In a medium bowl, beat the cream cheese with a hand mixer until smooth. Add the powdered sugar, vanilla, and salt, and beat until well combined and fluffy.
Spread or pipe the cream cheese frosting onto the cooled muffins.