Preheat the oven to 350°F (175°C). Line 18 muffin molds (1 ½ standard muffin pans) with paper liners or lightly grease the cups. In a large bowl, whisk together the flour, baking powder, baking soda, brown sugar, cinnamon, cardamom, nutmeg, and salt.
In a separate bowl, whisk together the grated zucchini, orange juice, plant-based milk, yogurt, vanilla extract, and neutral oil.
Pour the wet ingredients into the dry ingredients and stir just until no dry flour remains. Do not overmix.
Fold in the walnuts and chocolate chips, if using.
Divide the batter evenly among the 18 muffin cups, filling each nearly to the top.
In a small bowl, combine the flour, sugar, orange zest, and salt. Add the olive oil and mix with a fork until the mixture forms coarse, crumbly pieces. Set aside.
Sprinkle the olive oil streusel evenly over the muffins, gently pressing it into the batter so it stays in place during baking.
Bake for 24-26 minutes, or until the tops are golden and a toothpick inserted into the center of a muffin comes out clean or with a few moist crumbs. Let the muffins cool in the pan for 5 minutes, then transfer them to a wire rack to cool further.