Preheat the oven to 500°F (if using a baking sheet) or as high as it will go (if using a baking stone/steel; place the stone/steel in the oven before you start preheating).
Place a large skillet over medium heat and add the spinach. Cook the spinach for 5 minutes, working in batches if necessary, until it is completely wilted, then remove the pan from the heat and set it aside to cool.
Wipe out the skillet, add the oil, and warm it over medium-high heat. Toss in the scallions and cook for 3 minutes or until soft, stirring constantly.
Transfer the cooked scallions to a large bowl, and add the ricotta, ½ cup of the feta, the egg, dill, parsley, and nutmeg. Squeeze as much liquid as you can from the spinach, chop it up, and add the spinach to the bowl. Mix well and season with the salt.
If you're using a baking stone/steel, turn the oven to Broil on high.
Stretch or roll out your dough to a 12-inch circle, then transfer it to a baking sheet or a lightly floured pizza peel (if using a baking stone/steel).
Brush the dough with olive oil, making sure you get it all the way to the edges. Spoon the spinach mixture onto the dough and use your hands to spread it evenly, leaving a ½-inch border of dough all around. Scatter the remaining ¼ cup of feta over top, drizzle lightly with olive oil, and season with a few grinds of black pepper.
Transfer the pizza to the oven and bake until the crust is golden and the cheese has browned in spots—8 to 10 minutes on the baking sheet, 6 to 8 minutes on the baking stone/steel.
Remove the pizza from the oven, let it cool for a few minutes, then slice and serve.