In a large skillet, sauté the onion and scallions with olive oil for about 5 minutes, until soft and lightly browned. Stir in the spinach and continue to cook until it is limp, about 5 minutes. Add the salt, stir, and transfer the mixture into a fine mesh colander.
Squeeze the liquid out of the spinach mixture by pressing with a large spoon. Let the spinach cool down for 15 minutes (see “Note 1” below).
Preheat the oven to 325º F.
In a large bowl, mix the ricotta, feta, spinach mixture, dill, and eggs together.
Brush a 9×11 (or something close to these dimensions) baking dish with olive oil. Lay down a sheet of phyllo dough, letting it cover the sides of the dish. Brush it very lightly with olive oil and then lay the next phyllo sheet on top. Use 8 phyllo sheets to cover the bottom (see “Note 2” below).
Pour the filling onto the layered phyllo and spread evenly. Cover with the remaining 8 sheets of phyllo dough, following the same technique you used for the bottom layers. Fold the flaps or excess from the sides and brush them with olive oil (they will break and crumble, but that’s OK).
Bake the Spanakopita for about 40 minutes, until golden brown.