Preheat oven to 350 degrees. Spray or grease two muffin tins, or line with liners.
In a large bowl, whisk together the eggs, oil, and sugar until well combined.
Stir in the grated squash, rosemary, and lemon zest until well combined.
Add the flour, baking soda, salt, and baking powder and stir well, until all the dry ingredients are mixed in.
Fold in the nuts, if using.
Distribute the batter evenly among the muffin cups and bake for 20 minutes, or until a toothpick inserted into the middle of a muffin comes out clean. Cool completely on a cooling rack and store at room temperature in an airtight container for up to 3 days or freeze for up to 3 months.