Preheat your oven to 350°F (175°C). Line 18 muffin tins with paper liners or grease lightly.
In a large bowl or mixer, mix together the pumpkin puree, grated zucchini, oil, eggs, sugar, and water until smooth.
Add the eggs and make sure you mix them in thoroughly.
In a separate bowl, sift the flour, baking soda, baking powder, salt, cinnamon, nutmeg, and cloves.
Gradually add the dry mixture to the wet ingredients, stirring until just combined. Avoid overmixing to keep the muffins tender. Fold in any optional add-ins.
Scoop the batter into the muffin cups, filling each about 3/4 full. Bake for 25-30 minutes, or until a toothpick inserted in the center comes out clean.