In the oil, cook the onion and garlic until softened, about 3-4 minutes.
In a bowl, combine the cooked onion and garlic, ricotta, spinach, Parmesan cheese, lemon rind, nutmeg, salt, and pepper.
Cut the phyllo sheets into strips about 10 cm wide.
Lay out a strip of phyllo paper and baste it with the melted butter. Add 1-2 tbsp of the spinach filling , then fold up the paper in a triangular shape. Place on a baking sheet.
Bake at 375 °F until golden brown, about 19 minutes.