Preheat the oven to 350°F. Lightly oil a 9x13" baking dish.
Into a large skillet over medium heat, add the olive oil. When the oil is hot, add the yellow onion and scallions. Cook for 2 minutes, stirring frequently until softened. Add the garlic and continue cooking for an additional 1 minute.
Stir in the spinach and parsley. Continue cooking for 2 minutes, stirring frequently until the spinach is wilted. Remove from heat and set aside.
Into a medium-size mixing bowl, add the JustEgg vegan egg replacer and the vegan feta. Stir gently until just combined. Fold in the spinach mixture.
Into the prepared baking dish, place two sheets of phyllo dough and brush lightly to cover with olive oil. Add another 2 sheets and brush again with olive oil, then repeat with two more sheets of phyllo dough and olive oil. (Phyllo dough is very delicate and it's okay if it tears; just make sure you're covering the pan completely with each layer.)
Add the spinach and feta mixture, gently spreading to cover the phyllo dough.
Top with 4 additional sheets of phyllo dough, brushing with olive oil after each addition.
Bake for 40 minutes, until lightly crispy and golden brown. Allow to set for 10 minutes then slice and serve.