Preheat oven to 350° F. Grease a standard 12 muffin pan with melted butter or cooking spray. Set aside.

Make the pesto: in a food processor or blender, add the basil, parsley, garlic, pine nuts, lemon zest, lemon juice, salt and pepper, Pulse a few times until the mixture becomes coarse and chopped. Scrape down the sides of the bowl with a spatula and pulse once more. With the machine running, slowly pour in the olive oil and pulse briefly to make a coarse paste. The mixture should be thick and slightly creamy. Add the Parmesan and pulse once more to incorporate. Give the pesto a taste, if it is lacking in salt or pepper, add more to taste. Transfer the pesto to a bowl and set aside. It will yield about 1 cup of pesto.

To make the batter: in a large bowl, stir or sift together the flour, baking powder and salt. In a medium bowl, whisk together the eggs, olive oil, and milk. Stir in the thawed and squeezed-dried spinach into the wet ingredients. Make a well in the center of the dry ingredients, and pour the spinach mixture into the center. Fold the batter until evenly moistened. The batter will be slightly lumpy. Using a rubber spatula, fold in the pesto and mozzarella just until evenly distributed. Some streaks of pesto may remain, that will give the muffins color. Do not worry about mixing everything perfectly together. It is crucial to not overmix this batter as it will result in dry and tough muffins. Using an ice cream scoop or just a regular spoon, fill the muffin cups level with the rim.

Bake the muffins until golden brown, dry, and springy to the touch or until a toothpick inserted in the center comes out clean, about 20 to 25 minutes. Rotate the pan halfway through baking to ensure evening browning. Transfer the pan to a wire rack and let cool for 5 minutes. Carefully remove the muffins from the pan. Serve warm or at room temperature. Store any leftover muffins in an airtight container in the fridge. When ready to eat, warm through in a preheated 350°F oven for about 5 minutes. Enjoy!