Preheat your oven to 375°F (190°C) and grease and flour a 9x13-inch baking dish.

In a large mixing bowl, combine the flour, salt, baking powder, red pepper flakes, and oregano.

Add the eggs, milk, melted butter, onion, garlic, spinach, and shredded mozzarella cheese. Mix until fully incorporated.

Pour the batter evenly into the prepared baking dish.

Bake for 30–35 minutes, or until a toothpick inserted into the center comes out clean and the top is golden brown.

Allow to cool slightly before slicing into squares and serving.